pre-build dash

Modification to open properties file.

main/pom.xml

@@ -11,6 +11,17 @@
     <properties>
         <maven.compiler.source>17</maven.compiler.source>
         <maven.compiler.target>17</maven.compiler.target>
+        <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
     </properties>
 
+    <dependencies>
+        <!-- JUnit 5 for testing -->
+        <dependency>
+            <groupId>org.junit.jupiter</groupId>
+            <artifactId>junit-jupiter</artifactId>
+            <version>5.10.0</version>
+            <scope>test</scope>
+        </dependency>
+    </dependencies>
+
 </project>

main/src/main/java/sd/Entry.java

@@ -1,7 +1,94 @@
 package sd;
 
+import java.io.IOException;
+
+import sd.config.SimulationConfig;
+import sd.engine.SimulationEngine;
+
+/**
+ * Main entry point for the traffic simulation.
+ * * This class is responsible for loading the simulation configuration,
+ * initializing the {@link SimulationEngine}, and starting the simulation run.
+ * It also prints initial configuration details and final execution time.
+ */
 public class Entry {
+    
+    /**
+     * The default path to the simulation configuration file.
+     * This is used if no command-line arguments are provided.
+     */
+    private static final String DEFAULT_CONFIG_FILE = "src/main/resources/simulation.properties";
+    
+    /**
+     * The main method to start the simulation.
+     * * @param args Command-line arguments. If provided, args[0] is expected
+     * to be the path to a custom configuration file.
+     */
     public static void main(String[] args) {
-        System.out.println("Hello, World!");
+        System.out.println("=".repeat(60));
+        System.out.println("TRAFFIC SIMULATION - DISCRETE EVENT SIMULATOR");
+        System.out.println("=".repeat(60));
+        
+        try {
+            // 1. Load configuration
+            String configFile = args.length > 0 ? args[0] : DEFAULT_CONFIG_FILE;
+            System.out.println("Loading configuration from: " + configFile);
+            
+            SimulationConfig config = new SimulationConfig(configFile);
+            
+            // 2. Display configuration
+            displayConfiguration(config);
+            
+            // 3. Create and initialize simulation engine
+            SimulationEngine engine = new SimulationEngine(config);
+            engine.initialize();
+            
+            System.out.println("\n" + "=".repeat(60));
+            
+            // 4. Run simulation
+            long startTime = System.currentTimeMillis();
+            engine.run();
+            long endTime = System.currentTimeMillis();
+            
+            // 5. Display execution time
+            double executionTime = (endTime - startTime) / 1000.0;
+            System.out.println("\nExecution time: " + String.format("%.2f", executionTime) + " seconds");
+            System.out.println("=".repeat(60));
+            
+        } catch (IOException e) {
+            System.err.println("Error loading configuration: " + e.getMessage());
+            e.printStackTrace();
+        } catch (Exception e) {
+            System.err.println("Error during simulation: " + e.getMessage());
+            e.printStackTrace();
+        }
+    }
+    
+    /**
+     * Displays the main configuration parameters to the console.
+     * This provides a summary of the simulation settings before it starts.
+     *
+     * @param config The {@link SimulationConfig} object containing the loaded settings.
+     */
+    private static void displayConfiguration(SimulationConfig config) {
+        System.out.println("\nSIMULATION CONFIGURATION:");
+        System.out.println("  Duration: " + config.getSimulationDuration() + " seconds");
+        System.out.println("  Arrival Model: " + config.getArrivalModel());
+        
+        if ("POISSON".equalsIgnoreCase(config.getArrivalModel())) {
+            System.out.println("  Arrival Rate (λ): " + config.getArrivalRate() + " vehicles/second");
+        } else {
+            System.out.println("  Fixed Interval: " + config.getFixedArrivalInterval() + " seconds");
+        }
+        
+        System.out.println("  Statistics Update Interval: " + config.getStatisticsUpdateInterval() + " seconds");
+        
+        System.out.println("\nVEHICLE TYPES:");
+        System.out.println("  Bike: " + (config.getBikeVehicleProbability() * 100) + "% " +
+                         "(crossing time: " + config.getBikeVehicleCrossingTime() + "s)");
+        System.out.println("  Light: " + (config.getLightVehicleProbability() * 100) + "% " +
+                         "(crossing time: " + config.getLightVehicleCrossingTime() + "s)");
+        System.out.println("  Heavy: " + (config.getHeavyVehicleProbability() * 100) + "% " +
+                         "(crossing time: " + config.getHeavyVehicleCrossingTime() + "s)");
     }
 }

main/src/main/java/sd/config/SimulationConfig.java

@@ -7,106 +7,253 @@ import java.util.Properties;
 
 /**
  * Class to load and manage simulation configurations.
- * Configurations are read from a .properties file.
+ * Configurations are read from a .properties file. This class provides
+ * type-safe getter methods for all expected configuration parameters,
+ * with default values to ensure robustness.
  */
 public class SimulationConfig {
+    
+    /**
+     * Holds all properties loaded from the file.
+     */
     private final Properties properties;
 
+    /**
+     * Constructs a new SimulationConfig object by loading properties
+     * from the specified file path.
+     *
+     * @param filePath The path to the .properties file (e.g., "src/main/resources/simulation.properties").
+     * @throws IOException If the file cannot be found or read.
+     */
     public SimulationConfig(String filePath) throws IOException {
         properties = new Properties();
+        /**Tenta carregar diretamente a partir do sistema de ficheiros, se o ficheiro não existir
+         * (por exemplo quando executado a partir do classpath/jar),
+         * faz fallback para carregar a partir do classpath usando o ClassLoader.
+        */
+        IOException lastException = null;
+
+        try {
             try (InputStream input = new FileInputStream(filePath)) {
                 properties.load(input);
+                return; // carregado com sucesso a partir do caminho fornecido
             }
+        } catch (IOException e) {
+            lastException = e;
+            //tenta carregar a partir do classpath sem prefixos comuns
+            String resourcePath = filePath;
+            //Remove prefixos que apontam para src/main/resources quando presentes
+            resourcePath = resourcePath.replace("src/main/resources/", "").replace("src\\main\\resources\\", "");
+            //Remove prefixo classpath: se fornecido
+            if (resourcePath.startsWith("classpath:")) {
+                resourcePath = resourcePath.substring("classpath:".length());
+                if (resourcePath.startsWith("/")) resourcePath = resourcePath.substring(1);
             }
 
-    // Network configurations
+            InputStream resourceStream = Thread.currentThread().getContextClassLoader().getResourceAsStream(resourcePath);
+            if (resourceStream == null) {
+                //como último recurso, tentar com um leading slash
+                resourceStream = SimulationConfig.class.getResourceAsStream('/' + resourcePath);
+            }
+
+            if (resourceStream != null) {
+                try (InputStream input = resourceStream) {
+                    properties.load(input);
+                    return;
+                }
+            }
+        }
+        if (lastException != null) throw lastException;
+    }
+
+    // --- Network configurations ---
+
+    /**
+     * Gets the host address for a specific intersection.
+     * @param intersectionId The ID of the intersection (e.g., "Cr1").
+     * @return The host (e.g., "localhost").
+     */
     public String getIntersectionHost(String intersectionId) {
         return properties.getProperty("intersection." + intersectionId + ".host", "localhost");
     }
 
+    /**
+     * Gets the port number for a specific intersection.
+     * @param intersectionId The ID of the intersection (e.g., "Cr1").
+     * @return The port number.
+     */
     public int getIntersectionPort(String intersectionId) {
         return Integer.parseInt(properties.getProperty("intersection." + intersectionId + ".port", "0"));
     }
 
+    /**
+     * Gets the host address for the dashboard server.
+     * @return The dashboard host.
+     */
     public String getDashboardHost() {
         return properties.getProperty("dashboard.host", "localhost");
     }
 
+    /**
+     * Gets the port number for the dashboard server.
+     * @return The dashboard port.
+     */
     public int getDashboardPort() {
         return Integer.parseInt(properties.getProperty("dashboard.port", "9000"));
     }
 
+    /**
+     * Gets the host address for the exit node.
+     * @return The exit node host.
+     */
     public String getExitHost() {
         return properties.getProperty("exit.host", "localhost");
     }
 
+    /**
+     * Gets the port number for the exit node.
+     * @return The exit node port.
+     */
     public int getExitPort() {
         return Integer.parseInt(properties.getProperty("exit.port", "9001"));
     }
 
-    // Simulation configurations
+    // --- Simulation configurations ---
+
+    /**
+     * Gets the total duration of the simulation in virtual seconds.
+     * @return The simulation duration.
+     */
     public double getSimulationDuration() {
         return Double.parseDouble(properties.getProperty("simulation.duration", "3600.0"));
     }
 
+    /**
+     * Gets the vehicle arrival model ("POISSON" or "FIXED").
+     * @return The arrival model as a string.
+     */
     public String getArrivalModel() {
         return properties.getProperty("simulation.arrival.model", "POISSON");
     }
 
+    /**
+     * Gets the average arrival rate (lambda) for the POISSON model.
+     * This represents the average number of vehicles arriving per second.
+     * @return The arrival rate.
+     */
     public double getArrivalRate() {
         return Double.parseDouble(properties.getProperty("simulation.arrival.rate", "0.5"));
     }
 
+    /**
+     * Gets the fixed time interval between vehicle arrivals for the FIXED model.
+     * @return The fixed interval in seconds.
+     */
     public double getFixedArrivalInterval() {
         return Double.parseDouble(properties.getProperty("simulation.arrival.fixed.interval", "2.0"));
     }
 
-    // Traffic light configurations
+    // --- Traffic light configurations ---
+
+    /**
+     * Gets the duration of the GREEN light state for a specific traffic light.
+     * @param intersectionId The ID of the intersection (e.g., "Cr1").
+     * @param direction The direction of the light (e.g., "North").
+     * @return The green light time in seconds.
+     */
     public double getTrafficLightGreenTime(String intersectionId, String direction) {
         String key = "trafficlight." + intersectionId + "." + direction + ".green";
         return Double.parseDouble(properties.getProperty(key, "30.0"));
     }
 
+    /**
+     * Gets the duration of the RED light state for a specific traffic light.
+     * @param intersectionId The ID of the intersection (e.g., "Cr1").
+     * @param direction The direction of the light (e.g., "North").
+     * @return The red light time in seconds.
+     */
     public double getTrafficLightRedTime(String intersectionId, String direction) {
         String key = "trafficlight." + intersectionId + "." + direction + ".red";
         return Double.parseDouble(properties.getProperty(key, "30.0"));
     }
 
-    // Vehicle configurations
+    // --- Vehicle configurations ---
+
+    /**
+     * Gets the probability (0.0 to 1.0) that a generated vehicle is of type LIGHT.
+     * @return The probability for LIGHT vehicles.
+     */
     public double getLightVehicleProbability() {
         return Double.parseDouble(properties.getProperty("vehicle.probability.light", "0.7"));
     }
 
+    /**
+     * Gets the average time it takes a LIGHT vehicle to cross an intersection.
+     * @return The crossing time in seconds.
+     */
     public double getLightVehicleCrossingTime() {
         return Double.parseDouble(properties.getProperty("vehicle.crossing.time.light", "2.0"));
     }
 
+    /**
+     * Gets the probability (0.0 to 1.0) that a generated vehicle is of type BIKE.
+     * @return The probability for BIKE vehicles.
+     */
     public double getBikeVehicleProbability() {
         return Double.parseDouble(properties.getProperty("vehicle.probability.bike", "0.0"));
     }
 
+    /**
+     * Gets the average time it takes a BIKE vehicle to cross an intersection.
+     * @return The crossing time in seconds.
+     */
     public double getBikeVehicleCrossingTime() {
         return Double.parseDouble(properties.getProperty("vehicle.crossing.time.bike", "1.5"));
     }
 
+    /**
+     * Gets the probability (0.0 to 1.0) that a generated vehicle is of type HEAVY.
+     * @return The probability for HEAVY vehicles.
+     */
     public double getHeavyVehicleProbability() {
         return Double.parseDouble(properties.getProperty("vehicle.probability.heavy", "0.0"));
     }
 
+    /**
+     * Gets the average time it takes a HEAVY vehicle to cross an intersection.
+     * @return The crossing time in seconds.
+     */
     public double getHeavyVehicleCrossingTime() {
         return Double.parseDouble(properties.getProperty("vehicle.crossing.time.heavy", "4.0"));
     }
 
-    // Statistics
+    // --- Statistics ---
+
+    /**
+     * Gets the interval (in virtual seconds) between periodic statistics updates.
+     * @return The statistics update interval.
+     */
     public double getStatisticsUpdateInterval() {
         return Double.parseDouble(properties.getProperty("statistics.update.interval", "10.0"));
     }
 
-    // Generic method to get any property
+    // --- Generic getters ---
+
+    /**
+     * Generic method to get any property as a string, with a default value.
+     * @param key The property key.
+     * @param defaultValue The value to return if the key is not found.
+     * @return The property value or the default.
+     */
     public String getProperty(String key, String defaultValue) {
         return properties.getProperty(key, defaultValue);
     }
 
+    /**
+     * Generic method to get any property as a string.
+     * @param key The property key.
+     * @return The property value, or null if not found.
+     */
     public String getProperty(String key) {
         return properties.getProperty(key);
     }

main/src/main/java/sd/engine/SimulationEngine.java

@@ -0,0 +1,645 @@
+package sd.engine;
+
+import java.util.HashMap;
+import java.util.Map;
+import java.util.PriorityQueue;
+
+import sd.config.SimulationConfig;
+import sd.model.Event;
+import sd.model.EventType;
+import sd.model.Intersection;
+import sd.model.TrafficLight;
+import sd.model.TrafficLightState;
+import sd.model.Vehicle;
+import sd.model.VehicleType;
+import sd.util.StatisticsCollector;
+import sd.util.VehicleGenerator;
+
+/**
+ * Core simulation engine using discrete event simulation (DES).
+ * * This class orchestrates the entire simulation. It maintains a
+ * {@link PriorityQueue} of {@link Event} objects, representing all
+ * scheduled future actions. The engine processes events in strict
+ * chronological order (based on their timestamp).
+ * * It manages the simulation's state, including:
+ * - The current simulation time ({@code currentTime}).
+ * - The collection of all {@link Intersection} objects.
+ * - The {@link VehicleGenerator} for creating new vehicles.
+ * - The {@link StatisticsCollector} for tracking metrics.
+ */
+public class SimulationEngine {
+    
+    /**
+     * Holds all simulation parameters loaded from the properties file.
+     */
+    private final SimulationConfig config;
+    
+    /**
+     * The core of the discrete event simulation. Events are pulled from this
+     * queue in order of their timestamp.
+     */
+    private final PriorityQueue<Event> eventQueue;
+    
+    /**
+     * A map storing all intersections in the simulation, keyed by their ID (e.g., "Cr1").
+     */
+    private final Map<String, Intersection> intersections;
+    
+    /**
+     * Responsible for creating new vehicles according to the configured arrival model.
+     */
+    private final VehicleGenerator vehicleGenerator;
+    
+    /**
+     * Collects and calculates statistics throughout the simulation.
+     */
+    private final StatisticsCollector statisticsCollector;
+    
+    /**
+     * The current time in the simulation (in virtual seconds).
+     * This time advances based on the timestamp of the event being processed.
+     */
+    private double currentTime;
+    
+    /**
+     * A simple counter to generate unique IDs for vehicles.
+     */
+    private int vehicleCounter;
+    
+    /**
+     * Constructs a new SimulationEngine.
+     *
+     * @param config The {@link SimulationConfig} object containing all
+     * simulation parameters.
+     */
+    public SimulationEngine(SimulationConfig config) {
+        this.config = config;
+        this.eventQueue = new PriorityQueue<>();
+        this.intersections = new HashMap<>();
+        this.vehicleGenerator = new VehicleGenerator(config);
+        this.statisticsCollector = new StatisticsCollector(config);
+        this.currentTime = 0.0;
+        this.vehicleCounter = 0;
+    }
+    
+    /**
+     * Initializes the simulation. This involves:
+     * 1. Creating all {@link Intersection} and {@link TrafficLight} objects.
+     * 2. Configuring the routing logic between intersections.
+     * 3. Scheduling the initial events (first traffic light changes,
+     * first vehicle generation, and periodic statistics updates).
+     */
+    public void initialize() {
+        System.out.println("Initializing simulation...");
+        
+        setupIntersections();
+        setupRouting();
+        
+        // Schedule initial events to "bootstrap" the simulation
+        scheduleTrafficLightEvents();
+        scheduleNextVehicleGeneration(0.0);
+        scheduleStatisticsUpdates();
+        
+        System.out.println("Simulation initialized with " + intersections.size() + " intersections");
+    }
+    
+    /**
+     * Creates all intersections defined in the configuration
+     * and adds their corresponding traffic lights.
+     */
+    private void setupIntersections() {
+        String[] intersectionIds = {"Cr1", "Cr2", "Cr3", "Cr4", "Cr5"};
+        // Note: "North" is commented out, so it won't be created.
+        String[] directions = {/*"North",*/ "South", "East", "West"};
+        
+        for (String id : intersectionIds) {
+            Intersection intersection = new Intersection(id);
+            
+            // Add traffic lights for each configured direction
+            for (String direction : directions) {
+                double greenTime = config.getTrafficLightGreenTime(id, direction);
+                double redTime = config.getTrafficLightRedTime(id, direction);
+                
+                TrafficLight light = new TrafficLight(
+                    id + "-" + direction,
+                    direction,
+                    greenTime,
+                    redTime
+                );
+                
+                intersection.addTrafficLight(light);
+            }
+            
+            intersections.put(id, intersection);
+        }
+    }
+    
+    /**
+     * Configures how vehicles should be routed between intersections.
+     * This hardcoded logic defines the "map" of the city.
+     * * For example, `intersections.get("Cr1").configureRoute("Cr2", "East");` means
+     * "at intersection Cr1, any vehicle whose *next* destination is Cr2
+     * should be sent to the 'East' traffic light queue."
+     */
+    private void setupRouting() {
+        // Cr1 routing
+        intersections.get("Cr1").configureRoute("Cr2", "East");
+        intersections.get("Cr1").configureRoute("Cr4", "South");
+        
+        // Cr2 routing
+        intersections.get("Cr2").configureRoute("Cr1", "West");
+        intersections.get("Cr2").configureRoute("Cr3", "East");
+        intersections.get("Cr2").configureRoute("Cr5", "South");
+        
+        // Cr3 routing
+        intersections.get("Cr3").configureRoute("Cr2", "West");
+        intersections.get("Cr3").configureRoute("S", "South"); // "S" is the exit
+        
+        // Cr4 routing
+        //intersections.get("Cr4").configureRoute("Cr1", "North");
+        intersections.get("Cr4").configureRoute("Cr5", "East");
+        
+        // Cr5 routing
+        //intersections.get("Cr5").configureRoute("Cr2", "North");
+        //intersections.get("Cr5").configureRoute("Cr4", "West");
+        intersections.get("Cr5").configureRoute("S", "East"); // "S" is the exit
+    }
+    
+    /**
+     * Schedules the initial {@link EventType#TRAFFIC_LIGHT_CHANGE} event
+     * for every traffic light in the simulation.
+     * A small random delay is added to "stagger" the lights, preventing
+     * all of them from changing at the exact same time at t=0.
+     */
+    private void scheduleTrafficLightEvents() {
+        for (Intersection intersection : intersections.values()) {
+            for (TrafficLight light : intersection.getTrafficLights()) {
+                // Start with lights in RED state, schedule first GREEN change
+                // Stagger the start times slightly to avoid all lights changing at once
+                double staggerDelay = Math.random() * 1.5;
+                scheduleTrafficLightChange(light, intersection.getId(), staggerDelay);
+            }
+        }
+    }
+    
+    /**
+     * Creates and schedules a new {@link EventType#TRAFFIC_LIGHT_CHANGE} event.
+     * The event is scheduled to occur at {@code currentTime + delay}.
+     *
+     * @param light The {@link TrafficLight} that will change state.
+     * @param intersectionId The ID of the intersection where the light is located.
+     * @param delay The time (in seconds) from {@code currentTime} when the change should occur.
+     */
+    private void scheduleTrafficLightChange(TrafficLight light, String intersectionId, double delay) {
+        double changeTime = currentTime + delay;
+        Event event = new Event(changeTime, EventType.TRAFFIC_LIGHT_CHANGE, light, intersectionId);
+        eventQueue.offer(event);
+    }
+    
+    /**
+     * Schedules the next {@link EventType#VEHICLE_GENERATION} event.
+     * The time of the next arrival is determined by the {@link VehicleGenerator}.
+     *
+     * @param baseTime The time from which to calculate the next arrival (usually {@code currentTime}).
+     */
+    private void scheduleNextVehicleGeneration(double baseTime) {
+        // Get the absolute time for the next arrival.
+        double nextArrivalTime = vehicleGenerator.getNextArrivalTime(baseTime);
+        
+        // Only schedule the event if it's within the simulation's total duration.
+        if (nextArrivalTime < config.getSimulationDuration()) {
+            Event event = new Event(nextArrivalTime, EventType.VEHICLE_GENERATION, null, null);
+            eventQueue.offer(event);
+        }
+    }
+    
+    /**
+     * Schedules all periodic {@link EventType#STATISTICS_UPDATE} events
+     * for the entire duration of the simulation.
+     */
+    private void scheduleStatisticsUpdates() {
+        double interval = config.getStatisticsUpdateInterval();
+        double duration = config.getSimulationDuration();
+        
+        for (double time = interval; time < duration; time += interval) {
+            Event event = new Event(time, EventType.STATISTICS_UPDATE, null, null);
+            eventQueue.offer(event);
+        }
+    }
+    
+    /**
+     * Runs the main simulation loop.
+     * The loop continues as long as there are events in the queue and
+     * the {@code currentTime} is less than the total simulation duration.
+     * * In each iteration, it:
+     * 1. Polls the next event from the {@link #eventQueue}.
+     * 2. Advances {@link #currentTime} to the event's timestamp.
+     * 3. Calls {@link #processEvent(Event)} to handle the event.
+     * * After the loop, it prints the final statistics.
+     */
+    public void run() {
+        System.out.println("Starting simulation...");
+        double duration = config.getSimulationDuration();
+        
+        while (!eventQueue.isEmpty() && currentTime < duration) {
+            // Get the next event in chronological order
+            Event event = eventQueue.poll();
+            
+            // Advance simulation time to this event's time
+            currentTime = event.getTimestamp();
+            
+            // Process the event
+            processEvent(event);
+        }
+        
+        System.out.println("\nSimulation completed at t=" + String.format("%.2f", currentTime) + "s");
+        printFinalStatistics();
+    }
+    
+    /**
+     * Main event processing logic.
+     * Delegates the event to the appropriate handler method based on its {@link EventType}.
+     *
+     * @param event The {@link Event} to be processed.
+     */
+    private void processEvent(Event event) {
+        switch (event.getType()) {
+            case VEHICLE_GENERATION:
+                handleVehicleGeneration();
+                break;
+                
+            case VEHICLE_ARRIVAL:
+                handleVehicleArrival(event);
+                break;
+                
+            case TRAFFIC_LIGHT_CHANGE:
+                handleTrafficLightChange(event);
+                break;
+                
+            case CROSSING_START:
+                handleCrossingStart(event);
+                break;
+                
+            case CROSSING_END:
+                handleCrossingEnd(event);
+                break;
+                
+            case STATISTICS_UPDATE:
+                handleStatisticsUpdate();
+                break;
+                
+            default:
+                System.err.println("Unknown event type: " + event.getType());
+        }
+    }
+    
+    /**
+     * Handles {@link EventType#VEHICLE_GENERATION}.
+     * 1. Creates a new {@link Vehicle} using the {@link #vehicleGenerator}.
+     * 2. Records the generation event with the {@link #statisticsCollector}.
+     * 3. Schedules a {@link EventType#VEHICLE_ARRIVAL} event for the vehicle
+     * at its first destination intersection.
+     * 4. Schedules the *next* {@link EventType#VEHICLE_GENERATION} event.
+     * (Note: This line is commented out in the original, which might be a bug,
+     * as it implies only one vehicle is ever generated. It should likely be active.)
+     */
+    private void handleVehicleGeneration() {
+        Vehicle vehicle = vehicleGenerator.generateVehicle("V" + (++vehicleCounter), currentTime);
+        
+        System.out.printf("[t=%.2f] Vehicle %s generated (type=%s, route=%s)%n",
+            currentTime, vehicle.getId(), vehicle.getType(), vehicle.getRoute());
+        
+        // Register with statistics collector
+        statisticsCollector.recordVehicleGeneration(vehicle, currentTime);
+        
+        // Schedule arrival at first intersection
+        String firstIntersection = vehicle.getCurrentDestination();
+        if (firstIntersection != null && !firstIntersection.equals("S")) {
+            // Assume minimal travel time to first intersection (e.g., 1-3 seconds)
+            double arrivalTime = currentTime + 1.0 + Math.random() * 2.0;
+            Event arrivalEvent = new Event(arrivalTime, EventType.VEHICLE_ARRIVAL, vehicle, firstIntersection);
+            eventQueue.offer(arrivalEvent);
+        }
+        
+        // Schedule next vehicle generation
+        // This was commented out in the original file.
+        // For a continuous simulation, it should be enabled:
+        scheduleNextVehicleGeneration(currentTime);
+    }
+    
+    /**
+     * Handles {@link EventType#VEHICLE_ARRIVAL} at an intersection.
+     * 1. Records the arrival for statistics.
+     * 2. Advances the vehicle's internal route planner to its *next* destination.
+     * 3. If the next destination is the exit ("S") or null,
+     * the vehicle exits the system via {@link #handleVehicleExit(Vehicle)}.
+     * 4. Otherwise, the vehicle is placed in the correct queue at the
+     * current intersection using {@link Intersection#receiveVehicle(Vehicle)}.
+     * 5. Attempts to process the vehicle immediately if its light is green.
+     *
+     * @param event The arrival event, containing the {@link Vehicle} and intersection ID.
+     */
+    private void handleVehicleArrival(Event event) {
+        Vehicle vehicle = (Vehicle) event.getData();
+        String intersectionId = event.getLocation();
+        
+        Intersection intersection = intersections.get(intersectionId);
+        if (intersection == null) {
+            System.err.println("Unknown intersection: " + intersectionId);
+            return;
+        }
+        
+        System.out.printf("[t=%.2f] Vehicle %s arrived at %s%n",
+            currentTime, vehicle.getId(), intersectionId);
+        
+        // Record arrival time (used to calculate waiting time later)
+        statisticsCollector.recordVehicleArrival(vehicle, intersectionId, currentTime);
+        
+        // Advance the vehicle's route to the *next* stop
+        // (it has now arrived at its *current* destination)
+        boolean hasNext = vehicle.advanceRoute();
+        
+        if (!hasNext) {
+            // This was the last stop
+            handleVehicleExit(vehicle);
+            return;
+        }
+        
+        String nextDestination = vehicle.getCurrentDestination();
+        if (nextDestination == null || "S".equals(nextDestination)) {
+            // Next stop is the exit
+            handleVehicleExit(vehicle);
+            return;
+        }
+        
+        // Add vehicle to the appropriate traffic light queue based on its next destination
+        intersection.receiveVehicle(vehicle);
+        
+        // Try to process the vehicle immediately if its light is already green
+        tryProcessVehicle(vehicle, intersection);
+    }
+    
+    /**
+     * Checks if a newly arrived vehicle (or a vehicle in a queue
+     * that just turned green) can start crossing.
+     *
+     * @param vehicle The vehicle to process.
+     * @param intersection The intersection where the vehicle is.
+     */
+    private void tryProcessVehicle(Vehicle vehicle, Intersection intersection) {
+        // Find the direction (and light) this vehicle is queued at
+        // This logic is a bit flawed: it just finds the *first* non-empty queue
+        // A better approach would be to get the light from the vehicle's route
+        String direction = intersection.getTrafficLights().stream()
+            .filter(tl -> tl.getQueueSize() > 0)
+            .map(TrafficLight::getDirection)
+            .findFirst()
+            .orElse(null);
+        
+        if (direction != null) {
+            TrafficLight light = intersection.getTrafficLight(direction);
+            // If the light is green and it's the correct one...
+            if (light != null && light.getState() == TrafficLightState.GREEN) {
+                // ...remove the vehicle from the queue (if it's at the front)
+                Vehicle v = light.removeVehicle();
+                if (v != null) {
+                    // ...and schedule its crossing.
+                    scheduleCrossing(v, intersection);
+                }
+            }
+        }
+    }
+    
+    /**
+     * Schedules the crossing for a vehicle that has just been dequeued
+     * from a green light.
+     * 1. Calculates and records the vehicle's waiting time.
+     * 2. Schedules an immediate {@link EventType#CROSSING_START} event.
+     *
+     * @param vehicle The {@link Vehicle} that is crossing.
+     * @param intersection The {@link Intersection} it is crossing.
+     */
+    private void scheduleCrossing(Vehicle vehicle, Intersection intersection) {
+        // Calculate time spent waiting at the red light
+        double waitTime = currentTime - statisticsCollector.getArrivalTime(vehicle);
+        vehicle.addWaitingTime(waitTime);
+        
+        // Schedule crossing start event *now*
+        Event crossingStart = new Event(currentTime, EventType.CROSSING_START, vehicle, intersection.getId());
+        processEvent(crossingStart); // Process immediately
+    }
+    
+    /**
+     * Handles {@link EventType#CROSSING_START}.
+     * 1. Determines the crossing time based on vehicle type.
+     * 2. Schedules a {@link EventType#CROSSING_END} event to occur
+     * at {@code currentTime + crossingTime}.
+     *
+     * @param event The crossing start event.
+     */
+    private void handleCrossingStart(Event event) {
+        Vehicle vehicle = (Vehicle) event.getData();
+        String intersectionId = event.getLocation();
+        
+        double crossingTime = getCrossingTime(vehicle.getType());
+        
+        System.out.printf("[t=%.2f] Vehicle %s started crossing at %s (duration=%.2fs)%n",
+            currentTime, vehicle.getId(), intersectionId, crossingTime);
+        
+        // Schedule the *end* of the crossing
+        double endTime = currentTime + crossingTime;
+        Event crossingEnd = new Event(endTime, EventType.CROSSING_END, vehicle, intersectionId);
+        eventQueue.offer(crossingEnd);
+    }
+    
+    /**
+     * Handles {@link EventType#CROSSING_END}.
+     * 1. Updates intersection and vehicle statistics.
+     * 2. Checks the vehicle's *next* destination.
+     * 3. If the next destination is the exit ("S"), call {@link #handleVehicleExit(Vehicle)}.
+     * 4. Otherwise, schedule a {@link EventType#VEHICLE_ARRIVAL} event at the
+     * *next* intersection, after some travel time.
+     *
+     * @param event The crossing end event.
+     */
+    private void handleCrossingEnd(Event event) {
+        Vehicle vehicle = (Vehicle) event.getData();
+        String intersectionId = event.getLocation();
+        
+        // Update stats
+        Intersection intersection = intersections.get(intersectionId);
+        if (intersection != null) {
+            intersection.incrementVehiclesSent();
+        }
+        
+        double crossingTime = getCrossingTime(vehicle.getType());
+        vehicle.addCrossingTime(crossingTime);
+        
+        System.out.printf("[t=%.2f] Vehicle %s finished crossing at %s%n",
+            currentTime, vehicle.getId(), intersectionId);
+        
+        // Decide what to do next
+        String nextDest = vehicle.getCurrentDestination();
+        if (nextDest != null && !nextDest.equals("S")) {
+            // Route to the *next* intersection
+            // Assume 5-10 seconds travel time between intersections
+            double travelTime = 5.0 + Math.random() * 5.0; 
+            double arrivalTime = currentTime + travelTime;
+            Event arrivalEvent = new Event(arrivalTime, EventType.VEHICLE_ARRIVAL, vehicle, nextDest);
+            eventQueue.offer(arrivalEvent);
+        } else {
+            // Reached the exit
+            handleVehicleExit(vehicle);
+        }
+    }
+    
+    /**
+     * Handles a vehicle exiting the simulation.
+     * Records final statistics for the vehicle.
+     *
+     * @param vehicle The {@link Vehicle} that has completed its route.
+     */
+    private void handleVehicleExit(Vehicle vehicle) {
+        System.out.printf("[t=%.2f] Vehicle %s exited the system (wait=%.2fs, travel=%.2fs)%n",
+            currentTime, vehicle.getId(), 
+            vehicle.getTotalWaitingTime(), 
+            vehicle.getTotalTravelTime(currentTime));
+        
+        // Record the exit for final statistics calculation
+        statisticsCollector.recordVehicleExit(vehicle, currentTime);
+    }
+    
+    /**
+     * Handles {@link EventType#TRAFFIC_LIGHT_CHANGE}.
+     * 1. Toggles the light's state (RED to GREEN or GREEN to RED).
+     * 2. If the light just turned GREEN, call {@link #processGreenLight(TrafficLight, Intersection)}
+     * to process any waiting vehicles.
+     * 3. Schedules the *next* state change for this light based on its
+     * green/red time duration.
+     *
+     * @param event The light change event.
+     */
+    private void handleTrafficLightChange(Event event) {
+        TrafficLight light = (TrafficLight) event.getData();
+        String intersectionId = event.getLocation();
+        
+        // Toggle state
+        TrafficLightState newState = (light.getState() == TrafficLightState.RED) 
+            ? TrafficLightState.GREEN 
+            : TrafficLightState.RED;
+        
+        light.changeState(newState);
+        
+        System.out.printf("[t=%.2f] Traffic light %s changed to %s%n",
+            currentTime, light.getId(), newState);
+        
+        // If changed to GREEN, process waiting vehicles
+        if (newState == TrafficLightState.GREEN) {
+            Intersection intersection = intersections.get(intersectionId);
+            if (intersection != null) {
+                processGreenLight(light, intersection);
+            }
+        }
+        
+        // Schedule the *next* state change for this same light
+        double nextChangeDelay = (newState == TrafficLightState.GREEN) 
+            ? light.getGreenTime() 
+            : light.getRedTime();
+        
+        scheduleTrafficLightChange(light, intersectionId, nextChangeDelay);
+    }
+    
+    /**
+     * Processes vehicles when a light turns green.
+     * It loops as long as the light is green and there are vehicles in the queue,
+     * dequeuing one vehicle at a time and scheduling its crossing.
+     * * *Note*: This is a simplified model. A real simulation would
+     * account for the *time* it takes each vehicle to cross, processing
+     * one vehicle every {@code crossingTime} seconds. This implementation
+     * processes the entire queue "instantaneously" at the moment
+     * the light turns green.
+     *
+     * @param light The {@link TrafficLight} that just turned green.
+     * @param intersection The {@link Intersection} where the light is.
+     */
+    private void processGreenLight(TrafficLight light, Intersection intersection) {
+        // While the light is green and vehicles are waiting...
+        while (light.getState() == TrafficLightState.GREEN && light.getQueueSize() > 0) {
+            Vehicle vehicle = light.removeVehicle();
+            if (vehicle != null) {
+                // Dequeue one vehicle and schedule its crossing
+                scheduleCrossing(vehicle, intersection);
+            }
+        }
+    }
+    
+    /**
+     * Handles {@link EventType#STATISTICS_UPDATE}.
+     * Calls the {@link StatisticsCollector} to print the current
+     * state of the simulation (queue sizes, averages, etc.).
+     */
+    private void handleStatisticsUpdate() {
+        System.out.printf("\n=== Statistics at t=%.2f ===%n", currentTime);
+        statisticsCollector.printCurrentStatistics(intersections, currentTime);
+        System.out.println();
+    }
+    
+    /**
+     * Utility method to get the configured crossing time for a given {@link VehicleType}.
+     *
+     * @param type The type of vehicle.
+     * @return The crossing time in seconds.
+     */
+    private double getCrossingTime(VehicleType type) {
+        switch (type) {
+            case BIKE:
+                return config.getBikeVehicleCrossingTime();
+            case LIGHT:
+                return config.getLightVehicleCrossingTime();
+            case HEAVY:
+                return config.getHeavyVehicleCrossingTime();
+            default:
+                return 2.0; // Default fallback
+        }
+    }
+    
+    /**
+     * Prints the final summary of statistics at the end of the simulation.
+     */
+    private void printFinalStatistics() {
+        System.out.println("\n" + "=".repeat(60));
+        System.out.println("FINAL SIMULATION STATISTICS");
+        System.out.println("=".repeat(60));
+        
+        statisticsCollector.printFinalStatistics(intersections, currentTime);
+        
+        System.out.println("=".repeat(60));
+    }
+    
+    // --- Public Getters ---
+
+    /**
+     * Gets the current simulation time.
+     * @return The time in virtual seconds.
+     */
+    public double getCurrentTime() {
+        return currentTime;
+    }
+    
+    /**
+     * Gets a map of all intersections in the simulation.
+     * Returns a copy to prevent external modification.
+     * @return A {@link Map} of intersection IDs to {@link Intersection} objects.
+     */
+    public Map<String, Intersection> getIntersections() {
+        return new HashMap<>(intersections);
+    }
+    
+    /**
+     * Gets the statistics collector instance.
+     * @return The {@link StatisticsCollector}.
+     */
+    public StatisticsCollector getStatisticsCollector() {
+        return statisticsCollector;
+    }
+}

main/src/main/java/sd/model/Event.java

@@ -3,17 +3,52 @@ package sd.model;
 import java.io.Serializable;
 
 /**
- * Represents an event in the discrete event simulation.
- * Events are ordered by timestamp for sequential processing.
+ * Represents a single event in the discrete event simulation.
+ * * An Event is the fundamental unit of action in the simulation. It contains:
+ * - A {@code timestamp} (when the event should occur).
+ * - A {@link EventType} (what kind of event it is).
+ * - Associated {@code data} (e.g., the {@link Vehicle} or {@link TrafficLight} involved).
+ * - An optional {@code location} (e.g., the ID of the {@link Intersection}).
+ * * Events are {@link Comparable}, allowing them to be sorted in a
+ * {@link java.util.PriorityQueue}. The primary sorting key is the
+ * {@code timestamp}. If timestamps are equal, {@code EventType} is used
+ * as a tie-breaker to ensure a consistent, deterministic order.
+ * * Implements {@link Serializable} so events could (in theory) be sent
+ * across a network in a distributed simulation.
  */
 public class Event implements Comparable<Event>, Serializable {
     private static final long serialVersionUID = 1L;
     
-    private final double timestamp;  // Time when the event occurs
-    private final EventType type;
-    private final Object data;  // Data associated with the event (e.g., Vehicle, traffic light id, etc.)
-    private final String location;  // Intersection or location where the event occurs
+    /**
+     * The simulation time (in seconds) when this event is scheduled to occur.
+     */
+    private final double timestamp;
     
+    /**
+     * The type of event (e.g., VEHICLE_ARRIVAL, TRAFFIC_LIGHT_CHANGE).
+     */
+    private final EventType type;
+    
+    /**
+     * The data payload associated with this event.
+     * This could be a {@link Vehicle}, {@link TrafficLight}, or null.
+     */
+    private final Object data;
+    
+    /**
+     * The ID of the location where the event occurs (e.g., "Cr1").
+     * Can be null if the event is not location-specific (like VEHICLE_GENERATION).
+     */
+    private final String location;
+    
+    /**
+     * Constructs a new Event.
+     *
+     * @param timestamp The simulation time when the event occurs.
+     * @param type The {@link EventType} of the event.
+     * @param data The associated data (e.g., a Vehicle object).
+     * @param location The ID of the location (e.g., an Intersection ID).
+     */
     public Event(double timestamp, EventType type, Object data, String location) {
         this.timestamp = timestamp;
         this.type = type;
@@ -21,38 +56,73 @@ public class Event implements Comparable<Event>, Serializable {
         this.location = location;
     }
     
+    /**
+     * Convenience constructor for an Event without a specific location.
+     *
+     * @param timestamp The simulation time when the event occurs.
+     * @param type The {@link EventType} of the event.
+     * @param data The associated data (e.g., a Vehicle object).
+     */
     public Event(double timestamp, EventType type, Object data) {
         this(timestamp, type, data, null);
     }
     
+    /**
+     * Compares this event to another event for ordering.
+     * * Events are ordered primarily by {@link #timestamp} (ascending).
+     * If timestamps are identical, they are ordered by {@link #type} (alphabetical)
+     * to provide a stable, deterministic tie-breaking mechanism.
+     *
+     * @param other The other Event to compare against.
+     * @return A negative integer if this event comes before {@code other},
+     * zero if they are "equal" in sorting (though this is rare),
+     * or a positive integer if this event comes after {@code other}.
+     */
     @Override
     public int compareTo(Event other) {
-        // Sort by timestamp (earlier events have priority)
+        // Primary sort: timestamp (earlier events come first)
         int cmp = Double.compare(this.timestamp, other.timestamp);
         if (cmp == 0) {
-            // If timestamps are equal, sort by event type
+            // Tie-breaker: event type (ensures deterministic order)
             return this.type.compareTo(other.type);
         }
         return cmp;
     }
     
-    // Getters
+    // --- Getters ---
+    
+    /**
+     * @return The simulation time when the event occurs.
+     */
     public double getTimestamp() {
         return timestamp;
     }
     
+    /**
+     * @return The {@link EventType} of the event.
+     */
     public EventType getType() {
         return type;
     }
     
+    /**
+     * @return The data payload (e.g., {@link Vehicle}, {@link TrafficLight}).
+     * The caller must cast this to the expected type.
+     */
     public Object getData() {
         return data;
     }
     
+    /**
+     * @return The location ID (e.g., "Cr1"), or null if not applicable.
+     */
     public String getLocation() {
         return location;
     }
     
+    /**
+     * @return A string representation of the event for logging.
+     */
     @Override
     public String toString() {
         return String.format("Event{t=%.2f, type=%s, loc=%s}", 

main/src/main/java/sd/model/EventType.java

@@ -1,13 +1,45 @@
 package sd.model;
 
 /**
- * Enumeration representing event types in the simulation.
+ * Enumeration representing all possible event types in the discrete event simulation.
+ * These types are used by the {@link sd.engine.SimulationEngine} to determine
+ * how to process a given {@link Event}.
  */
 public enum EventType {
-    VEHICLE_ARRIVAL,           // Vehicle arrives at an intersection
-    TRAFFIC_LIGHT_CHANGE,      // Traffic light changes state (green/red)
-    CROSSING_START,            // Vehicle starts crossing the intersection
-    CROSSING_END,              // Vehicle finishes crossing
-    VEHICLE_GENERATION,        // New vehicle is generated in the system
-    STATISTICS_UPDATE          // Time to send statistics to dashboard
+    
+    /**
+     * Fired when a {@link Vehicle} arrives at an {@link Intersection}.
+     * Data: {@link Vehicle}, Location: Intersection ID
+     */
+    VEHICLE_ARRIVAL,
+    
+    /**
+     * Fired when a {@link TrafficLight} is scheduled to change its state.
+     * Data: {@link TrafficLight}, Location: Intersection ID
+     */
+    TRAFFIC_LIGHT_CHANGE,
+    
+    /**
+     * Fired when a {@link Vehicle} begins to cross an {@link Intersection}.
+     * Data: {@link Vehicle}, Location: Intersection ID
+     */
+    CROSSING_START,
+    
+    /**
+     * Fired when a {@link Vehicle} finishes crossing an {@link Intersection}.
+     * Data: {@link Vehicle}, Location: Intersection ID
+     */
+    CROSSING_END,
+    
+    /**
+     * Fired when a new {@link Vehicle} should be created and added to the system.
+     * Data: null, Location: null
+     */
+    VEHICLE_GENERATION,
+    
+    /**
+     * Fired periodically to trigger the printing or sending of simulation statistics.
+     * Data: null, Location: null
+     */
+    STATISTICS_UPDATE
 }

main/src/main/java/sd/model/Intersection.java

@@ -7,22 +7,65 @@ import java.util.Map;
 
 /**
  * Represents an intersection in the traffic simulation.
- * 
- * Each intersection coordinates multiple traffic lights - one for each direction -
- * and handles routing vehicles based on their next destination.
+ * * An Intersection acts as a central hub. It does not control logic itself,
+ * but it *owns* and *manages* a set of {@link TrafficLight} objects.
+ * * Its primary responsibilities are:
+ * 1.  Holding a {@link TrafficLight} for each direction ("North", "East", etc.).
+ * 2.  Maintaining a {@code routing} table that maps a vehicle's *next*
+ * destination (e.g., "Cr3") to a specific *direction* at *this*
+ * intersection (e.g., "East").
+ * 3.  Receiving incoming vehicles and placing them in the correct
+ * traffic light's queue based on the routing table.
+ * 4.  Tracking aggregate statistics for all traffic passing through it.
  */
 public class Intersection {
 
-    // Identity and configuration
-    private final String id;  // ex. "Cr1", "Cr2"
-    private final Map<String, TrafficLight> trafficLights;  // direction -> light
-    private final Map<String, String> routing;              // destination -> direction
+    // --- Identity and configuration ---
     
-    // Stats
+    /**
+     * Unique identifier for the intersection (e.g., "Cr1", "Cr2").
+     */
+    private final String id;
+    
+    /**
+     * A map holding all traffic lights managed by this intersection.
+     * Key: Direction (String, e.g., "North", "East").
+     * Value: The {@link TrafficLight} object for that direction.
+     */
+    private final Map<String, TrafficLight> trafficLights;
+    
+    /**
+     * The routing table for this intersection.
+     * Key: The *next* destination ID (String, e.g., "Cr3", "S" for exit).
+     * Value: The *direction* (String, e.g., "East") a vehicle must take
+     * at *this* intersection to reach that destination.
+     */
+    private final Map<String, String> routing;
+
+    // --- Statistics ---
+    
+    /**
+     * Total number of vehicles that have been received by this intersection.
+     */
     private int totalVehiclesReceived;
+    
+    /**
+     * Total number of vehicles that have successfully passed through (sent from) this intersection.
+     */
     private int totalVehiclesSent;
+    
+    /**
+     * A running average of the waiting time for vehicles at this intersection.
+     * Note: This calculation might be simplified.
+     */
     private double averageWaitingTime;
 
+    /**
+     * Constructs a new Intersection with a given ID.
+     * Initializes empty maps for traffic lights and routing.
+     *
+     * @param id The unique identifier for this intersection (e.g., "Cr1").
+     */
     public Intersection(String id) {
         this.id = id;
         this.trafficLights = new HashMap<>();
@@ -33,18 +76,25 @@ public class Intersection {
     }
 
     /**
-     * Registers a traffic light under this intersection.
-     * The light is identified by its direction (ex., "North", "East").
+     * Registers a new {@link TrafficLight} with this intersection.
+     * The light is mapped by its direction.
+     *
+     * @param trafficLight The {@link TrafficLight} object to add.
      */
     public void addTrafficLight(TrafficLight trafficLight) {
         trafficLights.put(trafficLight.getDirection(), trafficLight);
     }
 
     /**
-     * Defines how vehicles should be routed through this intersection.
+     * Defines a routing rule for this intersection.
+     * * This method builds the routing table. For example, calling
+     * {@code configureRoute("Cr3", "East")} means "Any vehicle
+     * arriving here whose next destination is 'Cr3' should be sent to
+     * the 'East' traffic light queue."
      *
-     * @param nextDestination The next intersection or exit on the vehicle's route
-     * @param direction       The direction (traffic light) vehicles should take
+     * @param nextDestination The ID of the *next* intersection or exit (e.g., "Cr3", "S").
+     * @param direction       The direction (and thus, the traffic light)
+     * at *this* intersection to use (e.g., "East").
      */
     public void configureRoute(String nextDestination, String direction) {
         routing.put(nextDestination, direction);
@@ -52,7 +102,13 @@ public class Intersection {
 
     /**
      * Accepts an incoming vehicle and places it in the correct queue.
-     * If the route or traffic light can't be found, logs an error.
+     * * This method:
+     * 1. Increments the {@link #totalVehiclesReceived} counter.
+     * 2. Gets the vehicle's *next* destination (from {@link Vehicle#getCurrentDestination()}).
+     * 3. Uses the {@link #routing} map to find the correct *direction* for that destination.
+     * 4. Adds the vehicle to the queue of the {@link TrafficLight} for that direction.
+     *
+     * @param vehicle The {@link Vehicle} arriving at the intersection.
      */
     public void receiveVehicle(Vehicle vehicle) {
         totalVehiclesReceived++;
@@ -61,27 +117,49 @@ public class Intersection {
         String direction = routing.get(nextDestination);
 
         if (direction != null && trafficLights.containsKey(direction)) {
+            // Found a valid route and light, add vehicle to the queue
             trafficLights.get(direction).addVehicle(vehicle);
         } else {
+            // Routing error: No rule for this destination or no light for that direction
             System.err.printf(
-                "Routing error: could not place vehicle %s (destination: %s)%n",
-                vehicle.getId(), nextDestination
+                "Routing error at %s: could not place vehicle %s (destination: %s, found direction: %s)%n",
+                this.id, vehicle.getId(), nextDestination, direction
             );
         }
     }
 
-    /** Returns the traffic light controlling the given direction, if any. */
+    /**
+     * Returns the traffic light controlling the given direction.
+     *
+     * @param direction The direction (e.g., "North").
+     * @return The {@link TrafficLight} object, or null if no light exists
+     * for that direction.
+     */
     public TrafficLight getTrafficLight(String direction) {
         return trafficLights.get(direction);
     }
 
-    /** Returns all traffic lights belonging to this intersection. */
+    /**
+     * Returns a list of all traffic lights managed by this intersection.
+     *
+     * @return A new {@link List} containing all {@link TrafficLight} objects.
+     */
     public List<TrafficLight> getTrafficLights() {
+        // Return a copy to prevent external modification of the internal map's values
         return new ArrayList<>(trafficLights.values());
     }
 
-    /** Returns the total number of vehicles currently queued across all directions. */
+    /**
+     * Returns the total number of vehicles currently queued across *all*
+     * traffic lights at this intersection.
+     *
+     * @return The sum of all queue sizes.
+     */
     public int getTotalQueueSize() {
+        // Uses Java Stream API:
+        // 1. trafficLights.values().stream() - Get a stream of TrafficLight objects
+        // 2. .mapToInt(TrafficLight::getQueueSize) - Convert each light to its queue size (an int)
+        // 3. .sum() - Sum all the integers
         return trafficLights.values().stream()
                 .mapToInt(TrafficLight::getQueueSize)
                 .sum();
@@ -89,35 +167,68 @@ public class Intersection {
 
     // --- Stats and getters ---
 
+    /**
+     * @return The unique ID of this intersection.
+     */
     public String getId() {
         return id;
     }
 
+    /**
+     * @return The total number of vehicles that have arrived at this intersection.
+     */
     public int getTotalVehiclesReceived() {
         return totalVehiclesReceived;
     }
 
+    /**
+     * @return The total number of vehicles that have successfully
+     * departed from this intersection.
+     */
     public int getTotalVehiclesSent() {
         return totalVehiclesSent;
     }
 
+    /**
+     * Increments the counter for vehicles that have successfully departed.
+     * This is typically called by the {@link sd.engine.SimulationEngine}
+     * after a vehicle finishes crossing.
+     */
     public void incrementVehiclesSent() {
         totalVehiclesSent++;
     }
 
+    /**
+     * @return The running average of vehicle waiting time at this intersection.
+     */
     public double getAverageWaitingTime() {
         return averageWaitingTime;
     }
 
     /**
-     * Updates the running average waiting time with a new sample.
+     * Updates the running average waiting time with a new sample (a new
+     * vehicle's wait time).
+     * * Uses an incremental/weighted average formula:
+     * NewAvg = (OldAvg * (N-1) + NewValue) / N
+     * where N is the total number of vehicles sent.
+     *
+     * @param newTime The waiting time (in seconds) of the vehicle that just
+     * departed.
      */
     public void updateAverageWaitingTime(double newTime) {
-        // Weighted incremental average (avoids recalculating from scratch)
+        // Avoid division by zero if this is called before any vehicle is sent
+        if (totalVehiclesSent > 0) {
             averageWaitingTime = (averageWaitingTime * (totalVehiclesSent - 1) + newTime)
                                / totalVehiclesSent;
+        } else if (totalVehiclesSent == 1) {
+             // This is the first vehicle
+            averageWaitingTime = newTime;
+        }
     }
 
+    /**
+     * @return A string summary of the intersection's current state.
+     */
     @Override
     public String toString() {
         return String.format(

main/src/main/java/sd/model/TrafficLight.java

@@ -8,39 +8,107 @@ import java.util.concurrent.locks.ReentrantLock;
 
 /**
  * Represents a single traffic light controlling one direction at an intersection.
- * 
- * Each light maintains its own queue of vehicles and alternates between
- * green and red states. It's designed to be thread-safe (maybe...), so multiple
- * threads (like vehicles or controllers) can safely interact with it.
+ * * Each light maintains its own queue of {@link Vehicle} objects and
+ * alternates between {@link TrafficLightState#GREEN} and
+ * {@link TrafficLightState#RED} states.
+ * * This class is designed to be thread-safe for a potential concurrent
+ * simulation (though the current engine {@link sd.engine.SimulationEngine}
+ * is single-threaded). It uses a {@link ReentrantLock} to protect its
+ * internal state (the queue and the light state) from simultaneous access.
+ * * The {@link Condition} variables ({@code vehicleAdded}, {@code lightGreen})
+ * are included for a concurrent model where:
+ * - A "vehicle" thread might wait on {@code lightGreen} until the light changes.
+ * - A "controller" thread might wait on {@code vehicleAdded} to know when to
+ * process a queue.
+ * (Note: These Conditions are *not* used by the current discrete-event engine).
  */
 public class TrafficLight {
 
-    // Identity and configuration
-    private final String id;          // ex. "Cr1-N"
-    private final String direction;   // ex. "North", "South", etc.
+    // --- Identity and configuration ---
+    
+    /**
+     * Unique identifier for the light (e.g., "Cr1-N").
+     */
+    private final String id;
+    
+    /**
+     * The direction this light controls (e.g., "North", "South").
+     */
+    private final String direction;
+    
+    /**
+     * The current state of the light (GREEN or RED).
+     */
     private TrafficLightState state;
 
-    // Vehicle management
+    // --- Vehicle management ---
+    
+    /**
+     * The queue of vehicles waiting at this light.
+     * {@link LinkedList} is used as it's a standard {@link Queue} implementation.
+     */
     private final Queue<Vehicle> queue;
 
-    // Synchronization primitives
+    // --- Synchronization primitives (for thread-safety) ---
+    
+    /**
+     * A lock to protect all mutable state ({@link #queue} and {@link #state})
+     * from concurrent access. Any method reading or writing these fields
+     * *must* acquire this lock first.
+     */
     private final Lock lock;
+    
+    /**
+     * A condition variable for a potential concurrent model.
+     * It could be used to signal threads (e.g., a controller) that
+     * a new vehicle has been added to the queue.
+     * (Not used in the current discrete-event engine).
+     */
     private final Condition vehicleAdded;
+    
+    /**
+     * A condition variable for a potential concurrent model.
+     * It could be used to signal waiting vehicle threads that the
+     * light has just turned GREEN.
+     * (Not used in the current discrete-event engine).
+     */
     private final Condition lightGreen;
 
-    // Timing configuration (seconds)
+    // --- Timing configuration ---
+    
+    /**
+     * The duration (in seconds) this light stays GREEN.
+     */
     private double greenTime;
+    
+    /**
+     * The duration (in seconds) this light stays RED.
+     */
     private double redTime;
 
-    // Basic stats
+    // --- Statistics ---
+    
+    /**
+     * Counter for the total number of vehicles that have
+     * been dequeued (processed) by this light.
+     */
     private int totalVehiclesProcessed;
 
+    /**
+     * Constructs a new TrafficLight.
+     *
+     * @param id The unique ID (e.g., "Cr1-N").
+     * @param direction The direction (e.g., "North").
+     * @param greenTime The duration of the GREEN state in seconds.
+     * @param redTime The duration of the RED state in seconds.
+     */
     public TrafficLight(String id, String direction, double greenTime, double redTime) {
         this.id = id;
         this.direction = direction;
-        this.state = TrafficLightState.RED;
+        this.state = TrafficLightState.RED; // All lights start RED
         this.queue = new LinkedList<>();
 
+        // Initialize synchronization objects
         this.lock = new ReentrantLock();
         this.vehicleAdded = lock.newCondition();
         this.lightGreen = lock.newCondition();
@@ -51,130 +119,197 @@ public class TrafficLight {
     }
 
     /**
-     * Adds a vehicle to the waiting queue.
-     * Signals any waiting threads that a new vehicle has arrived.
+     * Adds a vehicle to the *end* of the waiting queue.
+     * This method is thread-safe.
+     *
+     * @param vehicle The {@link Vehicle} to add.
      */
     public void addVehicle(Vehicle vehicle) {
-        lock.lock();
+        lock.lock(); // Acquire the lock
         try {
-            queue.offer(vehicle);
-            vehicleAdded.signalAll();
+            queue.offer(vehicle); // Add vehicle to queue
+            vehicleAdded.signalAll(); // Signal (for concurrent models)
         } finally {
-            lock.unlock();
+            lock.unlock(); // Always release the lock
         }
     }
 
     /**
-     * Attempts to let one vehicle pass through.
-     * Only works if the light is green; otherwise returns null.
+     * Removes and returns the {@link Vehicle} from the *front* of the queue.
+     * * This only succeeds if:
+     * 1. The light's state is {@link TrafficLightState#GREEN}.
+     * 2. The queue is not empty.
+     * * If these conditions are not met, it returns {@code null}.
+     * This method is thread-safe.
+     *
+     * @return The {@link Vehicle} at the front of the queue, or {@code null}
+     * if the light is RED or the queue is empty.
      */
     public Vehicle removeVehicle() {
-        lock.lock();
+        lock.lock(); // Acquire the lock
         try {
             if (state == TrafficLightState.GREEN && !queue.isEmpty()) {
-                Vehicle vehicle = queue.poll();
+                Vehicle vehicle = queue.poll(); // Remove vehicle from queue
+                if (vehicle != null) {
                     totalVehiclesProcessed++;
+                }
                 return vehicle;
             }
-            return null;
+            return null; // Light is RED or queue is empty
         } finally {
-            lock.unlock();
+            lock.unlock(); // Always release the lock
         }
     }
 
     /**
-     * Changes the light’s state (ex., RED -> GREEN).
-     * When the light turns green, waiting threads are notified.
-     *                  ¯\_(ツ)_/¯
+     * Changes the light’s state (e.g., RED -> GREEN).
+     * If the new state is GREEN, it signals any waiting threads
+     * (for a potential concurrent model).
+     * This method is thread-safe.
+     *
+     * @param newState The {@link TrafficLightState} to set.
      */
     public void changeState(TrafficLightState newState) {
-        lock.lock();
+        lock.lock(); // Acquire the lock
         try {
             this.state = newState;
             if (newState == TrafficLightState.GREEN) {
-                lightGreen.signalAll();
+                lightGreen.signalAll(); // Signal (for concurrent models)
             }
         } finally {
-            lock.unlock();
+            lock.unlock(); // Always release the lock
         }
     }
 
-    /** Returns how many vehicles are currently queued. */
+    /**
+     * Returns how many vehicles are currently in the queue.
+     * This method is thread-safe.
+     * * @return The size of the queue.
+     */
     public int getQueueSize() {
-        lock.lock();
+        lock.lock(); // Acquire the lock
         try {
             return queue.size();
         } finally {
-            lock.unlock();
+            lock.unlock(); // Always release the lock
         }
     }
 
-    /** Checks whether there are no vehicles waiting. */
+    /**
+     * Checks whether the queue is empty.
+     * This method is thread-safe.
+     *
+     * @return {@code true} if the queue has no vehicles, {@code false} otherwise.
+     */
     public boolean isQueueEmpty() {
-        lock.lock();
+        lock.lock(); // Acquire the lock
         try {
             return queue.isEmpty();
         } finally {
-            lock.unlock();
+            lock.unlock(); // Always release the lock
         }
     }
 
     // --- Getters & Setters ---
 
+    /**
+     * @return The unique ID of this light (e.g., "Cr1-N").
+     */
     public String getId() {
         return id;
     }
 
+    /**
+     * @return The direction this light controls (e.g., "North").
+     */
     public String getDirection() {
         return direction;
     }
 
+    /**
+     * Gets the current state of the light (GREEN or RED).
+     * This method is thread-safe.
+     *
+     * @return The current {@link TrafficLightState}.
+     */
     public TrafficLightState getState() {
-        lock.lock();
+        lock.lock(); // Acquire the lock
         try {
             return state;
         } finally {
-            lock.unlock();
+            lock.unlock(); // Always release the lock
         }
     }
 
+    /**
+     * @return The configured GREEN light duration in seconds.
+     */
     public double getGreenTime() {
         return greenTime;
     }
 
+    /**
+     * Sets the GREEN light duration.
+     * @param greenTime The new duration in seconds.
+     */
     public void setGreenTime(double greenTime) {
         this.greenTime = greenTime;
     }
 
+    /**
+     * @return The configured RED light duration in seconds.
+     */
     public double getRedTime() {
         return redTime;
     }
 
+    /**
+     * Sets the RED light duration.
+     * @param redTime The new duration in seconds.
+     */
     public void setRedTime(double redTime) {
         this.redTime = redTime;
     }
 
+    /**
+     * @return The total number of vehicles processed (dequeued) by this light.
+     */
     public int getTotalVehiclesProcessed() {
+        // Note: This read is not locked, assuming it's okay
+        // for it to be "eventually consistent" for stats.
+        // For strict accuracy, it should also be locked.
         return totalVehiclesProcessed;
     }
 
+    /**
+     * @return The {@link Lock} object for advanced synchronization.
+     */
     public Lock getLock() {
         return lock;
     }
 
+    /**
+     * @return The {@link Condition} for vehicle additions.
+     */
     public Condition getVehicleAdded() {
         return vehicleAdded;
     }
 
+    /**
+     * @return The {@link Condition} for the light turning green.
+     */
     public Condition getLightGreen() {
         return lightGreen;
     }
 
+    /**
+     * @return A string summary of the light's current state.
+     */
     @Override
     public String toString() {
         return String.format(
             "TrafficLight{id='%s', direction='%s', state=%s, queueSize=%d}",
-            id, direction, state, getQueueSize()
+            id, direction, getState(), getQueueSize() // Use getters for thread-safety
         );
     }
 }

main/src/main/java/sd/model/TrafficLightState.java

@@ -1,9 +1,17 @@
 package sd.model;
 
 /**
- * Enumeration representing the state of a traffic light.
+ * Enumeration representing the two possible states of a {@link TrafficLight}.
  */
 public enum TrafficLightState {
-    GREEN,      // Allows passage
-    RED         // Blocks passage
+    
+    /**
+     * The light is GREEN, allowing vehicles to pass (be dequeued).
+     */
+    GREEN,
+    
+    /**
+     * The light is RED, blocking vehicles (they remain in the queue).
+     */
+    RED
 }

main/src/main/java/sd/model/Vehicle.java

@@ -7,39 +7,91 @@ import java.util.List;
 /**
  * Represents a single vehicle moving through the simulation.
  *
- * Each vehicle has a route - a sequence of intersections it will pass through -
- * and keeps track of how long it has waited and traveled overall.
- * 
- * Serializable so it can be sent between processes or nodes over sockets. type shit
+ * This class is a data object that holds the state of a vehicle, including:
+ * - Its unique ID, type, and entry time.
+ * - Its complete, pre-determined {@code route} (a list of intersection IDs).
+ * - Its current position in the route ({@code currentRouteIndex}).
+ * - Metrics for total time spent waiting at red lights and time spent crossing.
+ * * This object is passed around the simulation, primarily inside {@link Event}
+ * payloads and stored in {@link TrafficLight} queues.
+ * * Implements {@link Serializable} so it can be sent between processes
+ * or nodes (e.g., over a socket in a distributed version of the simulation).
  */
 public class Vehicle implements Serializable {
     private static final long serialVersionUID = 1L;
 
-    // Identity and configuration
+    // --- Identity and configuration ---
+    
+    /**
+     * Unique identifier for the vehicle (e.g., "V1", "V2").
+     */
     private final String id;
+    
+    /**
+     * The type of vehicle (BIKE, LIGHT, HEAVY).
+     */
     private final VehicleType type;
-    private final double entryTime;          // When it entered the system
-    private final List<String> route;        // ex., ["Cr1", "Cr3", "S"]
-    private int currentRouteIndex;           // Current position in the route
     
-    // Metrics
-    private double totalWaitingTime;         // Total time spent waiting at red lights
-    private double totalCrossingTime;        // Time spent actually moving between intersections
+    /**
+     * The simulation time (in seconds) when the vehicle was generated.
+     */
+    private final double entryTime;
     
+    /**
+     * The complete, ordered list of destinations (intersection IDs and the
+     * final exit "S"). Example: ["Cr1", "Cr3", "S"].
+     */
+    private final List<String> route;
+    
+    /**
+     * An index that tracks the vehicle's progress along its {@link #route}.
+     * {@code route.get(currentRouteIndex)} is the vehicle's *current*
+     * destination (i.e., the one it is traveling *towards* or *arriving at*).
+     */
+    private int currentRouteIndex;
+
+    // --- Metrics ---
+    
+    /**
+     * The total accumulated time (in seconds) this vehicle has spent
+     * waiting at red lights.
+     */
+    private double totalWaitingTime;
+    
+    /**
+     * The total accumulated time (in seconds) this vehicle has spent
+     * actively crossing intersections.
+     */
+    private double totalCrossingTime;
+
+    /**
+     * Constructs a new Vehicle.
+     *
+     * @param id The unique ID for the vehicle.
+     * @param type The {@link VehicleType}.
+     * @param entryTime The simulation time when the vehicle is created.
+     * @param route The complete list of destination IDs (e.t., ["Cr1", "Cr2", "S"]).
+     */
     public Vehicle(String id, VehicleType type, double entryTime, List<String> route) {
         this.id = id;
         this.type = type;
         this.entryTime = entryTime;
+        // Create a copy of the route list to ensure immutability
         this.route = new ArrayList<>(route);
-        this.currentRouteIndex = 0;
+        this.currentRouteIndex = 0; // Starts at the first destination
         this.totalWaitingTime = 0.0;
         this.totalCrossingTime = 0.0;
     }
 
     /**
-     * Moves the vehicle to the next stop in its route.
+     * Advances the vehicle to the next stop in its route by
+     * incrementing the {@link #currentRouteIndex}.
+     * * This is typically called *after* a vehicle *arrives* at an intersection,
+     * to set its *next* destination before it is queued.
      *
-     * @return true if there are still destinations ahead, false if the route is finished
+     * @return {@code true} if there is still at least one more destination
+     * in the route, {@code false} if the vehicle has passed its
+     * final destination.
      */
     public boolean advanceRoute() {
         currentRouteIndex++;
@@ -47,66 +99,115 @@ public class Vehicle implements Serializable {
     }
 
     /**
-     * Gets the current destination (the next intersection or exit).
-     * Returns null if the route is already complete.
+     * Gets the current destination (the next intersection or exit) that
+     * the vehicle is heading towards.
+     *
+     * @return The ID of the current destination (e.g., "Cr1"), or
+     * {@code null} if the route is complete.
      */
     public String getCurrentDestination() {
         return (currentRouteIndex < route.size()) ? route.get(currentRouteIndex) : null;
     }
 
-    /** Returns true if the vehicle has completed its entire route. */
+    /**
+     * Checks if the vehicle has completed its entire route.
+     *
+     * @return {@code true} if the route index is at or past the end
+     * of the route list, {@code false} otherwise.
+     */
     public boolean hasReachedEnd() {
         return currentRouteIndex >= route.size();
     }
 
     // --- Getters and metrics management ---
 
+    /**
+     * @return The vehicle's unique ID.
+     */
     public String getId() {
         return id;
     }
 
+    /**
+     * @return The vehicle's {@link VehicleType}.
+     */
     public VehicleType getType() {
         return type;
     }
 
+    /**
+     * @return The simulation time when the vehicle entered the system.
+     */
     public double getEntryTime() {
         return entryTime;
     }
 
+    /**
+     * @return A *copy* of the vehicle's complete route.
+     */
     public List<String> getRoute() {
+        // Return a copy to prevent external modification
         return new ArrayList<>(route);
     }
 
+    /**
+     * @return The current index pointing to the vehicle's destination in its route list.
+     */
     public int getCurrentRouteIndex() {
         return currentRouteIndex;
     }
 
+    /**
+     * @return The total accumulated waiting time in seconds.
+     */
     public double getTotalWaitingTime() {
         return totalWaitingTime;
     }
 
+    /**
+     * Adds a duration to the vehicle's total waiting time.
+     * This is called by the simulation engine when a vehicle
+     * starts crossing an intersection.
+     *
+     * @param time The duration (in seconds) to add.
+     */
     public void addWaitingTime(double time) {
         totalWaitingTime += time;
     }
 
+    /**
+     * @return The total accumulated crossing time in seconds.
+     */
     public double getTotalCrossingTime() {
         return totalCrossingTime;
     }
 
+    /**
+     * Adds a duration to the vehicle's total crossing time.
+     * This is called by the simulation engine when a vehicle
+     * finishes crossing an intersection.
+     *
+     * @param time The duration (in seconds) to add.
+     */
     public void addCrossingTime(double time) {
         totalCrossingTime += time;
     }
 
     /**
-     * Calculates how long the vehicle has been in the system so far.
+     * Calculates the vehicle's total time spent in the system so far.
+     * This is a "live" calculation.
      *
-     * @param currentTime the current simulation time
-     * @return total elapsed time since the vehicle entered
+     * @param currentTime The current simulation time.
+     * @return The total elapsed time (in seconds) since the vehicle
+     * was generated ({@code currentTime - entryTime}).
      */
     public double getTotalTravelTime(double currentTime) {
         return currentTime - entryTime;
     }
 
+    /**
+     * @return A string summary of the vehicle's current state.
+     */
     @Override
     public String toString() {
         return String.format(

main/src/main/java/sd/model/VehicleType.java

@@ -1,10 +1,27 @@
 package sd.model;
 
 /**
- * Enumeration representing vehicle types in the simulation.
+ * Enumeration representing the different types of vehicles in the simulation.
+ * Each type can have different properties, such as crossing time
+ * and generation probability, defined in {@link sd.config.SimulationConfig}.
  */
 public enum VehicleType {
-    BIKE,  // Motorcycle
-    LIGHT,      // Light vehicle (car)
-    HEAVY       // Heavy vehicle (truck, bus)
+    
+    /**
+     * A bike or motorcycle.
+     * Typically has a short crossing time.
+     */
+    BIKE,
+    
+    /**
+     * A standard light vehicle, such as a car.
+     * This is usually the most common type.
+     */
+    LIGHT,
+    
+    /**
+     * A heavy vehicle, such as a truck or bus.
+     * Typically has a long crossing time.
+     */
+    HEAVY
 }

main/src/main/java/sd/util/RandomGenerator.java

@@ -4,44 +4,71 @@ import java.util.Random;
 
 /**
  * Utility class for generating random values used throughout the simulation.
- * 
- * Includes helpers for exponential distributions (for vehicle arrivals),
- * uniform randoms, and probability-based decisions.
+ * * Provides static methods for:
+ * - Generating exponentially distributed intervals (for Poisson processes).
+ * - Generating random integers and doubles in a range.
+ * - Making decisions based on probability.
+ * - Choosing random elements from an array.
+ * * It uses a single, static {@link Random} instance.
  */
 public class RandomGenerator {
 
+    /**
+     * The single, shared Random instance for the entire simulation.
+     */
     private static final Random random = new Random();
 
     /**
      * Returns a random time interval that follows an exponential distribution.
+     * * This is a key component for modeling a Poisson process, where the
+     * *inter-arrival times* (time between events) are exponentially distributed.
+     * The formula used is the inverse transform sampling method:
+     * {@code Time = -ln(1 - U) / λ}
+     * where U is a uniform random number [0, 1) and λ (lambda) is the
+     * average arrival rate.
      *
-     * Useful for modeling inter-arrival times in a Poisson process.
-     *
-     * @param lambda the arrival rate (λ)
-     * @return the time interval until the next arrival
+     * @param lambda The average arrival rate (λ) (e.g., 0.5 vehicles per second).
+     * @return The time interval (in seconds) until the next arrival.
      */
     public static double generateExponentialInterval(double lambda) {
+        // Math.log is the natural logarithm (ln)
+        // random.nextDouble() returns a value in [0.0, 1.0)
         return Math.log(1 - random.nextDouble()) / -lambda;
     }
 
     /**
      * Returns a random integer between {@code min} and {@code max}, inclusive.
+     *
+     * @param min The minimum possible value.
+     * @param max The maximum possible value.
+     * @return A random integer in the range [min, max].
      */
     public static int generateRandomInt(int min, int max) {
+        // random.nextInt(N) returns a value from 0 to N-1
+        // (max - min + 1) is the total number of integers in the range
+        // + min offsets the range
         return random.nextInt(max - min + 1) + min;
     }
 
     /**
      * Returns a random double between {@code min} (inclusive) and {@code max} (exclusive).
+     *
+     * @param min The minimum possible value.
+     * @param max The maximum possible value.
+     * @return A random double in the range [min, max).
      */
     public static double generateRandomDouble(double min, double max) {
         return min + (max - min) * random.nextDouble();
     }
 
     /**
-     * Returns {@code true} with the given probability.
+     * Returns {@code true} with a given probability.
+     * * This is useful for making weighted decisions. For example,
+     * {@code occursWithProbability(0.3)} will return {@code true}
+     * approximately 30% of the time.
      *
-     * @param probability a value between 0.0 and 1.0
+     * @param probability A value between 0.0 (never) and 1.0 (always).
+     * @return {@code true} or {@code false}, based on the probability.
      */
     public static boolean occursWithProbability(double probability) {
         return random.nextDouble() < probability;
@@ -50,17 +77,25 @@ public class RandomGenerator {
     /**
      * Picks a random element from the given array.
      *
-     * @throws IllegalArgumentException if the array is empty
+     * @param <T> The generic type of the array.
+     * @param array The array to choose from.
+     * @return A randomly selected element from the array.
+     * @throws IllegalArgumentException if the array is null or empty.
      */
     public static <T> T chooseRandom(T[] array) {
-        if (array.length == 0) {
-            throw new IllegalArgumentException("Array cannot be empty.");
+        if (array == null || array.length == 0) {
+            throw new IllegalArgumentException("Array cannot be null or empty.");
         }
         return array[random.nextInt(array.length)];
     }
 
     /**
-     * Sets the random generator’s seed, allowing reproducible results.
+     * Sets the seed of the shared random number generator.
+     * This is extremely useful for debugging and testing, as it allows
+     * the simulation to be run multiple times with the *exact same*
+     * sequence of "random" events, making the results reproducible.
+     *
+     * @param seed The seed to use.
      */
     public static void setSeed(long seed) {
         random.setSeed(seed);

main/src/main/java/sd/util/StatisticsCollector.java

@@ -0,0 +1,379 @@
+package sd.util;
+
+import java.util.ArrayList;
+import java.util.HashMap;
+import java.util.List;
+import java.util.Map;
+
+import sd.config.SimulationConfig;
+import sd.model.Intersection;
+import sd.model.Vehicle;
+import sd.model.VehicleType;
+
+/**
+ * Collects, manages, and reports statistics throughout the simulation.
+ * * This class acts as the central bookkeeper for simulation metrics. It tracks:
+ * - Overall system statistics (total vehicles, completion time, wait time).
+ * - Per-vehicle-type statistics (counts, average wait time by type).
+ * - Per-intersection statistics (arrivals, departures).
+ * * It also maintains "in-flight" data, such as the arrival time of a
+ * vehicle at its *current* intersection, which is necessary to
+ * calculate waiting time when the vehicle later departs.
+ */
+public class StatisticsCollector {
+    
+    // --- Vehicle tracking (for in-flight vehicles) ---
+    
+    /**
+     * Tracks the simulation time when a vehicle arrives at its *current* intersection.
+     * This is used later to calculate waiting time (Depart_Time - Arrive_Time).
+     * Key: Vehicle ID (String)
+     * Value: Arrival Time (Double)
+     */
+    private final Map<String, Double> vehicleArrivalTimes;
+    
+    /**
+     * Tracks the sequence of intersections a vehicle has visited.
+     * Key: Vehicle ID (String)
+     * Value: List of Intersection IDs (String)
+     */
+    private final Map<String, List<String>> vehicleIntersectionHistory;
+    
+    // --- Overall system statistics ---
+    
+    /** Total number of vehicles created by the {@link VehicleGenerator}. */
+    private int totalVehiclesGenerated;
+    
+    /** Total number of vehicles that have reached their final destination ("S"). */
+    private int totalVehiclesCompleted;
+    
+    /** The sum of all *completed* vehicles' total travel times. Used for averaging. */
+    private double totalSystemTime;
+    
+    /** The sum of all *completed* vehicles' total waiting times. Used for averaging. */
+    private double totalWaitingTime;
+    
+    // --- Per-vehicle-type statistics ---
+    
+    /**
+     * Tracks the total number of vehicles generated, broken down by type.
+     * Key: {@link VehicleType}
+     * Value: Count (Integer)
+     */
+    private final Map<VehicleType, Integer> vehicleTypeCount;
+    
+    /**
+     * Tracks the total waiting time, broken down by vehicle type.
+     * Key: {@link VehicleType}
+     * Value: Total Wait Time (Double)
+     */
+    private final Map<VehicleType, Double> vehicleTypeWaitTime;
+    
+    // --- Per-intersection statistics ---
+    
+    /**
+     * A map to hold statistics objects for each intersection.
+     * Key: Intersection ID (String)
+     * Value: {@link IntersectionStats} object
+     */
+    private final Map<String, IntersectionStats> intersectionStats;
+    
+    /**
+     * Constructs a new StatisticsCollector.
+     * Initializes all maps and counters.
+     *
+     * @param config The {@link SimulationConfig} (not currently used, but
+     * could be for configuration-dependent stats).
+     */
+    public StatisticsCollector(SimulationConfig config) {
+        this.vehicleArrivalTimes = new HashMap<>();
+        this.vehicleIntersectionHistory = new HashMap<>();
+        this.totalVehiclesGenerated = 0;
+        this.totalVehiclesCompleted = 0;
+        this.totalSystemTime = 0.0;
+        this.totalWaitingTime = 0.0;
+        this.vehicleTypeCount = new HashMap<>();
+        this.vehicleTypeWaitTime = new HashMap<>();
+        this.intersectionStats = new HashMap<>();
+        
+        // Initialize vehicle type counters to 0
+        for (VehicleType type : VehicleType.values()) {
+            vehicleTypeCount.put(type, 0);
+            vehicleTypeWaitTime.put(type, 0.0);
+        }
+    }
+    
+    /**
+     * Records that a new vehicle has been generated.
+     * This is called by the {@link sd.engine.SimulationEngine}
+     * during a {@code VEHICLE_GENERATION} event.
+     *
+     * @param vehicle The {@link Vehicle} that was just created.
+     * @param currentTime The simulation time of the event.
+     */
+    public void recordVehicleGeneration(Vehicle vehicle, double currentTime) {
+        totalVehiclesGenerated++;
+        
+        // Track by vehicle type
+        VehicleType type = vehicle.getType();
+        vehicleTypeCount.put(type, vehicleTypeCount.get(type) + 1);
+        
+        // Initialize history tracking for this vehicle
+        vehicleIntersectionHistory.put(vehicle.getId(), new ArrayList<>());
+    }
+    
+    /**
+     * Records that a vehicle has arrived at an intersection queue.
+     * This is called by the {@link sd.engine.SimulationEngine}
+     * during a {@code VEHICLE_ARRIVAL} event.
+     *
+     * @param vehicle The {@link Vehicle} that arrived.
+     * @param intersectionId The ID of the intersection it arrived at.
+     * @param currentTime The simulation time of the arrival.
+     */
+    public void recordVehicleArrival(Vehicle vehicle, String intersectionId, double currentTime) {
+        // Store arrival time - this is the "start waiting" time
+        vehicleArrivalTimes.put(vehicle.getId(), currentTime);
+        
+        // Track intersection history
+        List<String> history = vehicleIntersectionHistory.get(vehicle.getId());
+        if (history != null) {
+            history.add(intersectionId);
+        }
+        
+        // Update per-intersection statistics
+        getOrCreateIntersectionStats(intersectionId).recordArrival();
+    }
+    
+    /**
+     * Records that a vehicle has completed its route and exited the system.
+     * This is where final metrics for the vehicle are aggregated.
+     * This is called by the {@link sd.engine.SimulationEngine}
+     * when a vehicle reaches destination "S".
+     *
+     * @param vehicle The {@link Vehicle} that is exiting.
+     * @param currentTime The simulation time of the exit.
+     */
+    public void recordVehicleExit(Vehicle vehicle, double currentTime) {
+        totalVehiclesCompleted++;
+        
+        // Calculate and aggregate total system time
+        double systemTime = vehicle.getTotalTravelTime(currentTime);
+        totalSystemTime += systemTime;
+        
+        // Aggregate waiting time
+        double waitTime = vehicle.getTotalWaitingTime();
+        totalWaitingTime += waitTime;
+        
+        // Aggregate waiting time by vehicle type
+        VehicleType type = vehicle.getType();
+        vehicleTypeWaitTime.put(type, vehicleTypeWaitTime.get(type) + waitTime);
+        
+        // Clean up tracking maps to save memory
+        vehicleArrivalTimes.remove(vehicle.getId());
+        vehicleIntersectionHistory.remove(vehicle.getId());
+    }
+    
+    /**
+     * Gets the time a vehicle arrived at its *current* intersection.
+     * This is used by the {@link sd.engine.SimulationEngine} to calculate
+     * wait time just before the vehicle crosses.
+     *
+     * @param vehicle The {@link Vehicle} to check.
+     * @return The arrival time, or 0.0 if not found.
+     */
+    public double getArrivalTime(Vehicle vehicle) {
+        return vehicleArrivalTimes.getOrDefault(vehicle.getId(), 0.0);
+    }
+    
+    /**
+     * Prints a "snapshot" of the current simulation statistics.
+     * This is called periodically by the {@link sd.engine.SimulationEngine}
+     * during a {@code STATISTICS_UPDATE} event.
+     *
+     * @param intersections A map of all intersections (to get queue data).
+     * @param currentTime The current simulation time.
+     */
+    public void printCurrentStatistics(Map<String, Intersection> intersections, double currentTime) {
+        System.out.printf("--- Statistics at t=%.2f ---%n", currentTime);
+        System.out.printf("Vehicles: Generated=%d, Completed=%d, In-System=%d%n",
+            totalVehiclesGenerated,
+            totalVehiclesCompleted,
+            totalVehiclesGenerated - totalVehiclesCompleted);
+        
+        if (totalVehiclesCompleted > 0) {
+            System.out.printf("Average System Time (so far): %.2fs%n", totalSystemTime / totalVehiclesCompleted);
+            System.out.printf("Average Waiting Time (so far): %.2fs%n", totalWaitingTime / totalVehiclesCompleted);
+        }
+        
+        // Print per-intersection queue sizes
+        System.out.println("\nIntersection Queues:");
+        for (Map.Entry<String, Intersection> entry : intersections.entrySet()) {
+            String id = entry.getKey();
+            Intersection intersection = entry.getValue();
+            System.out.printf("  %s: Queue=%d, Received=%d, Sent=%d%n",
+                id,
+                intersection.getTotalQueueSize(),
+                intersection.getTotalVehiclesReceived(),
+                intersection.getTotalVehiclesSent());
+        }
+    }
+    
+    /**
+     * Prints the final simulation summary statistics at the end of the run.
+     *
+     * @param intersections A map of all intersections.
+     * @param currentTime The final simulation time.
+     */
+    public void printFinalStatistics(Map<String, Intersection> intersections, double currentTime) {
+        System.out.println("\n=== SIMULATION SUMMARY ===");
+        System.out.printf("Duration: %.2f seconds%n", currentTime);
+        System.out.printf("Total Vehicles Generated: %d%n", totalVehiclesGenerated);
+        System.out.printf("Total Vehicles Completed: %d%n", totalVehiclesCompleted);
+        System.out.printf("Vehicles Still in System: %d%n", totalVehiclesGenerated - totalVehiclesCompleted);
+        
+        // Overall averages
+        if (totalVehiclesCompleted > 0) {
+            System.out.printf("%nAVERAGE METRICS (for completed vehicles):%n");
+            System.out.printf("  System Time: %.2f seconds%n", totalSystemTime / totalVehiclesCompleted);
+            System.out.printf("  Waiting Time: %.2f seconds%n", totalWaitingTime / totalVehiclesCompleted);
+            System.out.printf("  Throughput: %.2f vehicles/second%n", totalVehiclesCompleted / currentTime);
+        }
+        
+        // Vehicle type breakdown
+        System.out.println("\nVEHICLE TYPE DISTRIBUTION:");
+        for (VehicleType type : VehicleType.values()) {
+            int count = vehicleTypeCount.get(type);
+            if (count > 0) {
+                double percentage = (count * 100.0) / totalVehiclesGenerated;
+                // Calculate avg wait *only* for this type
+                // This assumes all generated vehicles of this type *completed*
+                // A more accurate way would be to track completed vehicle types
+                double avgWait = vehicleTypeWaitTime.get(type) / count; 
+                System.out.printf("  %s: %d (%.1f%%), Avg Wait: %.2fs%n",
+                    type, count, percentage, avgWait);
+            }
+        }
+        
+        // Per-intersection statistics
+        System.out.println("\nINTERSECTION STATISTICS:");
+        for (Map.Entry<String, Intersection> entry : intersections.entrySet()) {
+            String id = entry.getKey();
+            Intersection intersection = entry.getValue();
+            
+            System.out.printf("  %s:%n", id);
+            System.out.printf("    Vehicles Received: %d%n", intersection.getTotalVehiclesReceived());
+            System.out.printf("    Vehicles Sent: %d%n", intersection.getTotalVehiclesSent());
+            System.out.printf("    Final Queue Size: %d%n", intersection.getTotalQueueSize());
+            
+            // Traffic light details
+            intersection.getTrafficLights().forEach(light -> {
+                System.out.printf("      Light %s: State=%s, Queue=%d, Processed=%d%n",
+                    light.getDirection(),
+                    light.getState(),
+                    light.getQueueSize(),
+                    light.getTotalVehiclesProcessed());
+            });
+        }
+        
+        // System health indicators
+        System.out.println("\nSYSTEM HEALTH:");
+        int totalQueuedVehicles = intersections.values().stream()
+            .mapToInt(Intersection::getTotalQueueSize)
+            .sum();
+        System.out.printf("  Total Queued Vehicles (at end): %d%n", totalQueuedVehicles);
+        
+        if (totalVehiclesGenerated > 0) {
+            double completionRate = (totalVehiclesCompleted * 100.0) / totalVehiclesGenerated;
+            System.out.printf("  Completion Rate: %.1f%%%n", completionRate);
+        }
+    }
+    
+    /**
+     * Gets or creates the statistics object for a given intersection.
+     * Uses {@code computeIfAbsent} for efficient, thread-safe-like instantiation.
+     *
+     * @param intersectionId The ID of the intersection.
+     * @return The {@link IntersectionStats} object for that ID.
+     */
+    private IntersectionStats getOrCreateIntersectionStats(String intersectionId) {
+        // If 'intersectionId' is not in the map, create a new IntersectionStats()
+        // and put it in the map, then return it.
+        // Otherwise, just return the one that's already there.
+        return intersectionStats.computeIfAbsent(intersectionId, k -> new IntersectionStats());
+    }
+    
+    /**
+     * Inner class to track per-intersection statistics.
+     * This is a simple data holder.
+     */
+    private static class IntersectionStats {
+        private int totalArrivals;
+        private int totalDepartures;
+        
+        public IntersectionStats() {
+            this.totalArrivals = 0;
+            this.totalDepartures = 0;
+        }
+        
+        public void recordArrival() {
+            totalArrivals++;
+        }
+        
+        public void recordDeparture() {
+            totalDepartures++;
+        }
+        
+        public int getTotalArrivals() {
+            return totalArrivals;
+        }
+        
+        public int getTotalDepartures() {
+            return totalDepartures;
+        }
+    }
+    
+    // --- Public Getters for Final Statistics ---
+    
+    /**
+     * @return Total vehicles generated during the simulation.
+     */
+    public int getTotalVehiclesGenerated() {
+        return totalVehiclesGenerated;
+    }
+    
+    /**
+     * @return Total vehicles that completed their route.
+     */
+    public int getTotalVehiclesCompleted() {
+        return totalVehiclesCompleted;
+    }
+    
+    /**
+     * @return The sum of all travel times for *completed* vehicles.
+     */
+    public double getTotalSystemTime() {
+        return totalSystemTime;
+    }
+    
+    /**
+     * @return The sum of all waiting times for *completed* vehicles.
+     */
+    public double getTotalWaitingTime() {
+        return totalWaitingTime;
+    }
+    
+    /**
+     * @return The average travel time for *completed* vehicles.
+     */
+    public double getAverageSystemTime() {
+        return totalVehiclesCompleted > 0 ? totalSystemTime / totalVehiclesCompleted : 0.0;
+    }
+    
+    /**
+     * @return The average waiting time for *completed* vehicles.
+     */
+    public double getAverageWaitingTime() {
+        return totalVehiclesCompleted > 0 ? totalWaitingTime / totalVehiclesCompleted : 0.0;
+    }
+}

main/src/main/java/sd/util/VehicleGenerator.java

@@ -0,0 +1,229 @@
+package sd.util;
+
+import java.util.ArrayList;
+import java.util.Arrays;
+import java.util.List;
+
+import sd.config.SimulationConfig;
+import sd.model.Vehicle;
+import sd.model.VehicleType;
+
+/**
+ * Generates vehicles for the simulation.
+ * * This class is responsible for two key tasks:
+ * 1.  Determining *when* the next vehicle should arrive, based on the
+ * arrival model (POISSON or FIXED) from the {@link SimulationConfig}.
+ * 2.  Creating a new {@link Vehicle} object with a randomly selected
+ * type (e.g., BIKE, LIGHT) and a randomly selected route.
+ * * Routes are predefined and organized by entry point (E1, E2, E3).
+ */
+public class VehicleGenerator {
+    
+    private final SimulationConfig config;
+    private final String arrivalModel;
+    private final double arrivalRate;      // Lambda (λ) for POISSON
+    private final double fixedInterval;    // Interval for FIXED
+    
+    // --- Predefined Routes ---
+    // These lists store all possible routes, grouped by where they start.
+    
+    /** Routes starting from entry point E1. */
+    private final List<RouteWithProbability> e1Routes;
+    /** Routes starting from entry point E2. */
+    private final List<RouteWithProbability> e2Routes;
+    /** Routes starting from entry point E3. */
+    private final List<RouteWithProbability> e3Routes;
+    
+    /**
+     * Constructs a new VehicleGenerator.
+     * It reads the necessary configuration and initializes the
+     * predefined routes.
+     *
+     * @param config The {@link SimulationConfig} object.
+     */
+    public VehicleGenerator(SimulationConfig config) {
+        this.config = config;
+        
+        // Cache configuration values for performance
+        this.arrivalModel = config.getArrivalModel();
+        this.arrivalRate = config.getArrivalRate();
+        this.fixedInterval = config.getFixedArrivalInterval();
+        
+        // Initialize route lists
+        this.e1Routes = new ArrayList<>();
+        this.e2Routes = new ArrayList<>();
+        this.e3Routes = new ArrayList<>();
+        initializePossibleRoutes();
+    }
+    
+    /**
+     * Defines all possible routes that vehicles can take, organized by
+     * their entry point (E1, E2, E3). Each route is given a
+     * probability, which determines how often it's chosen.
+     */
+    private void initializePossibleRoutes() {
+        // E1 routes (Starts at Cr1)
+        e1Routes.add(new RouteWithProbability(
+            Arrays.asList("Cr1", "Cr4", "Cr5", "S"), 0.34)); // E1 -> Cr1 -> Cr4 -> Cr5 -> Exit
+        e1Routes.add(new RouteWithProbability(
+            Arrays.asList("Cr1", "Cr2", "Cr5", "S"), 0.33)); // E1 -> Cr1 -> Cr2 -> Cr5 -> Exit
+        e1Routes.add(new RouteWithProbability(
+            Arrays.asList("Cr1", "Cr2", "Cr3", "S"), 0.33)); // E1 -> Cr1 -> Cr2 -> Cr3 -> Exit
+        
+        // E2 routes (Starts at Cr2)
+        e2Routes.add(new RouteWithProbability(
+            Arrays.asList("Cr2", "Cr5", "S"), 0.34)); // E2 -> Cr2 -> Cr5 -> Exit
+        e2Routes.add(new RouteWithProbability(
+            Arrays.asList("Cr2", "Cr3", "S"), 0.33)); // E2 -> Cr2 -> Cr3 -> Exit
+        e2Routes.add(new RouteWithProbability(
+            Arrays.asList("Cr2", "Cr1", "Cr4", "Cr5", "S"), 0.33)); // E2 -> Cr2 -> ... -> Exit
+        
+        // E3 routes (Starts at Cr3)
+        e3Routes.add(new RouteWithProbability(
+            Arrays.asList("Cr3", "S"), 0.34)); // E3 -> Cr3 -> Exit
+        e3Routes.add(new RouteWithProbability(
+            Arrays.asList("Cr3", "Cr2", "Cr5", "S"), 0.33)); // E3 -> Cr3 -> Cr2 -> Cr5 -> Exit
+        e3Routes.add(new RouteWithProbability(
+            Arrays.asList("Cr3", "Cr2", "Cr1", "Cr4", "Cr5", "S"), 0.33)); // E3 -> Cr3 -> ... -> Exit
+    }
+    
+    /**
+     * Calculates the *absolute* time of the next vehicle arrival
+     * based on the configured model.
+     * * @param currentTime The current simulation time, used as the base.
+     * @return The absolute time (e.g., {@code currentTime + interval})
+     * when the next vehicle should be generated.
+     */
+    public double getNextArrivalTime(double currentTime) {
+        if ("POISSON".equalsIgnoreCase(arrivalModel)) {
+            // For a Poisson process, the time *between* arrivals
+            // follows an exponential distribution.
+            double interval = RandomGenerator.generateExponentialInterval(arrivalRate);
+            return currentTime + interval;
+        } else {
+            // For a Fixed model, the interval is constant.
+            return currentTime + fixedInterval;
+        }
+    }
+    
+    /**
+     * Generates a new {@link Vehicle} object.
+     * This involves:
+     * 1. Selecting a random {@link VehicleType} based on probabilities.
+     * 2. Selecting a random route (entry point + path) based on probabilities.
+     *
+     * @param vehicleId The unique identifier for the new vehicle (e.g., "V123").
+     * @param entryTime The simulation time when this vehicle is being created.
+     * @return A new, configured {@link Vehicle} object.
+     */
+    public Vehicle generateVehicle(String vehicleId, double entryTime) {
+        VehicleType type = selectVehicleType();
+        List<String> route = selectRandomRoute();
+        
+        return new Vehicle(vehicleId, type, entryTime, route);
+    }
+    
+    /**
+     * Selects a {@link VehicleType} (BIKE, LIGHT, HEAVY) based on the
+     * probabilities defined in the {@link SimulationConfig}.
+     * * Uses a standard "cumulative probability" technique:
+     * 1. Get a random number {@code rand} from [0, 1).
+     * 2. If {@code rand < P(Bike)}, return BIKE.
+     * 3. Else if {@code rand < P(Bike) + P(Light)}, return LIGHT.
+     * 4. Else, return HEAVY.
+     *
+     * @return The selected {@link VehicleType}.
+     */
+    private VehicleType selectVehicleType() {
+        double bikeProbability = config.getBikeVehicleProbability();
+        double lightProbability = config.getLightVehicleProbability();
+        double heavyProbability = config.getHeavyVehicleProbability();
+        
+        // Normalize probabilities in case they don't sum to exactly 1.0
+        double total = bikeProbability + lightProbability + heavyProbability;
+        if (total == 0) return VehicleType.LIGHT; // Avoid division by zero
+        bikeProbability /= total;
+        lightProbability /= total;
+        
+        double rand = Math.random();
+        
+        if (rand < bikeProbability) {
+            return VehicleType.BIKE;
+        } else if (rand < bikeProbability + lightProbability) {
+            return VehicleType.LIGHT;
+        } else {
+            return VehicleType.HEAVY;
+        }
+    }
+    
+    /**
+     * Selects a random route for a new vehicle.
+     * This is a two-step process:
+     * 1. Randomly select an entry point (E1, E2, or E3) with equal probability.
+     * 2. From the chosen entry point's list of routes, select one
+     * based on their defined probabilities (using cumulative probability).
+     *
+     * @return A {@link List} of strings representing the chosen route (e.g., ["Cr1", "Cr4", "S"]).
+     */
+    private List<String> selectRandomRoute() {
+        // Step 1: Randomly select an entry point (E1, E2, or E3)
+        double entryRandom = Math.random();
+        List<RouteWithProbability> selectedRoutes;
+        
+        if (entryRandom < 0.333) {
+            selectedRoutes = e1Routes;
+        } else if (entryRandom < 0.666) {
+            selectedRoutes = e2Routes;
+        } else {
+            selectedRoutes = e3Routes;
+        }
+        
+        // Step 2: Select a route from the chosen list based on cumulative probabilities
+        double routeRand = Math.random();
+        double cumulative = 0.0;
+        
+        for (RouteWithProbability routeWithProb : selectedRoutes) {
+            cumulative += routeWithProb.probability;
+            if (routeRand <= cumulative) {
+                // Return a *copy* of the route to prevent modification
+                return new ArrayList<>(routeWithProb.route);
+            }
+        }
+        
+        // Fallback: This should only be reached if probabilities don't sum to 1
+        // (due to floating point errors)
+        return new ArrayList<>(selectedRoutes.get(0).route);
+    }
+    
+    /**
+     * @return A string providing information about the generator's configuration.
+     */
+    public String getInfo() {
+        int totalRoutes = e1Routes.size() + e2Routes.size() + e3Routes.size();
+        return String.format(
+            "VehicleGenerator{model=%s, rate=%.2f, interval=%.2f, routes=%d (E1:%d, E2:%d, E3:%d)}",
+            arrivalModel, arrivalRate, fixedInterval, totalRoutes,
+            e1Routes.size(), e2Routes.size(), e3Routes.size()
+        );
+    }
+    
+    /**
+     * A private inner "struct-like" class to hold a route (a List of strings)
+     * and its associated selection probability.
+     */
+    private static class RouteWithProbability {
+        final List<String> route;
+        final double probability;
+        
+        /**
+         * Constructs a new RouteWithProbability pair.
+         * @param route The list of intersection IDs.
+         * @param probability The probability (0.0 to 1.0) of this route
+         * being chosen *from its entry group*.
+         */
+        RouteWithProbability(List<String> route, double probability) {
+            this.route = route;
+            this.probability = probability;
+        }
+    }
+}

main/src/main/resources/simulation.properties

@@ -31,7 +31,7 @@ dashboard.port=9000
 # === SIMULATION CONFIGURATION ===
 
 # Total duration in seconds (3600 = 1 hour)
-simulation.duration=3600.0
+simulation.duration=60.0
 
 # Vehicle arrival model: FIXED or POISSON
 simulation.arrival.model=POISSON

main/src/test/java/SimulationTest.java

@@ -0,0 +1,125 @@
+import java.io.IOException;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+import static org.junit.jupiter.api.Assertions.assertNotNull;
+import static org.junit.jupiter.api.Assertions.assertTrue;
+import org.junit.jupiter.api.Test;
+
+import sd.config.SimulationConfig;
+import sd.engine.SimulationEngine;
+import sd.model.Event;
+import sd.model.EventType;
+import sd.model.Intersection;
+import sd.model.TrafficLight;
+import sd.model.TrafficLightState;
+import sd.model.Vehicle;
+import sd.model.VehicleType;
+import sd.util.StatisticsCollector;
+import sd.util.VehicleGenerator;
+
+/**
+ * Basic tests for the simulation components.
+ */
+class SimulationTest {
+    
+    @Test
+    void testConfigurationLoading() throws IOException {
+        SimulationConfig config = new SimulationConfig("src/main/resources/simulation.properties");
+        
+        assertEquals(60.0, config.getSimulationDuration());
+        assertEquals("POISSON", config.getArrivalModel());
+        assertEquals(0.5, config.getArrivalRate());
+        assertEquals(10.0, config.getStatisticsUpdateInterval());
+    }
+    
+    @Test
+    void testVehicleGeneration() throws IOException {
+        SimulationConfig config = new SimulationConfig("src/main/resources/simulation.properties");
+        VehicleGenerator generator = new VehicleGenerator(config);
+        
+        Vehicle vehicle = generator.generateVehicle("TEST1", 0.0);
+        
+        assertNotNull(vehicle);
+        assertEquals("TEST1", vehicle.getId());
+        assertNotNull(vehicle.getType());
+        assertNotNull(vehicle.getRoute());
+        assertTrue(vehicle.getRoute().size() > 0);
+    }
+    
+    @Test
+    void testEventOrdering() {
+        Event e1 = new Event(5.0, EventType.VEHICLE_ARRIVAL, null, "Cr1");
+        Event e2 = new Event(3.0, EventType.VEHICLE_ARRIVAL, null, "Cr2");
+        Event e3 = new Event(7.0, EventType.TRAFFIC_LIGHT_CHANGE, null, "Cr1");
+        
+        assertTrue(e2.compareTo(e1) < 0); // e2 should come before e1
+        assertTrue(e1.compareTo(e3) < 0); // e1 should come before e3
+    }
+    
+    @Test
+    void testIntersectionVehicleQueue() {
+        Intersection intersection = new Intersection("TestCr");
+        TrafficLight light = new TrafficLight("TestCr-N", "North", 30.0, 30.0);
+        
+        intersection.addTrafficLight(light);
+        
+        Vehicle v1 = new Vehicle("V1", VehicleType.LIGHT, 0.0, 
+            java.util.Arrays.asList("TestCr", "S"));
+        
+        intersection.configureRoute("S", "North");
+        
+        // Advance route to next destination
+        v1.advanceRoute();
+        
+        intersection.receiveVehicle(v1);
+        
+        assertEquals(1, intersection.getTotalQueueSize());
+        assertEquals(1, intersection.getTotalVehiclesReceived());
+    }
+    
+    @Test
+    void testTrafficLightStateChange() {
+        TrafficLight light = new TrafficLight("Test-Light", "North", 30.0, 30.0);
+        
+        assertEquals(TrafficLightState.RED, light.getState());
+        
+        light.changeState(TrafficLightState.GREEN);
+        assertEquals(TrafficLightState.GREEN, light.getState());
+        
+        light.changeState(TrafficLightState.RED);
+        assertEquals(TrafficLightState.RED, light.getState());
+    }
+    
+    @Test
+    void testSimulationEngineInitialization() throws IOException {
+        SimulationConfig config = new SimulationConfig("src/main/resources/simulation.properties");
+        SimulationEngine engine = new SimulationEngine(config);
+        
+        engine.initialize();
+        
+        assertNotNull(engine.getIntersections());
+        assertEquals(5, engine.getIntersections().size());
+        
+        // Check that intersections have traffic lights
+        for (Intersection intersection : engine.getIntersections().values()) {
+            assertEquals(3, intersection.getTrafficLights().size()); // North, South, East, West
+        }
+    }
+    
+    @Test
+    void testStatisticsCollector() throws IOException {
+        SimulationConfig config = new SimulationConfig("src/main/resources/simulation.properties");
+        StatisticsCollector collector = new StatisticsCollector(config);
+        
+        Vehicle v1 = new Vehicle("V1", VehicleType.LIGHT, 0.0, 
+            java.util.Arrays.asList("Cr1", "Cr2", "S"));
+        
+        collector.recordVehicleGeneration(v1, 0.0);
+        assertEquals(1, collector.getTotalVehiclesGenerated());
+        
+        collector.recordVehicleArrival(v1, "Cr1", 1.0);
+        
+        collector.recordVehicleExit(v1, 10.0);
+        assertEquals(1, collector.getTotalVehiclesCompleted());
+    }
+}