🏁 Single-Process Prototype — Implementation Summary

Status: ✅ Complete Date: October 22, 2025 Branch: 8-single-process-prototype

Overview

The single-process prototype implements a discrete event simulation (DES) of a 3×3 urban grid with five intersections, realistic vehicle behavior, and fully synchronized traffic lights. Everything runs under one process, laying the groundwork for the distributed architecture in Phase 3.

Core Architecture

SimulationEngine

Drives the DES loop with a priority queue of timestamped events — vehicles, lights, crossings, and periodic stats updates. Handles five intersections (Cr1–Cr5) and six event types.

Main loop:

while (events && time < duration):
    event = nextEvent()
    time = event.timestamp
    handle(event)

VehicleGenerator

Spawns vehicles via:

Poisson arrivals (λ = 0.5 veh/s) or fixed intervals
Probabilistic routes from E1–E3
Type distribution: 20% BIKE, 60% LIGHT, 20% HEAVY

StatisticsCollector

Tracks system-wide and per-type metrics: throughput, avg. wait, queue sizes, light cycles — updated every 10 s and at simulation end.

Model Highlights

Vehicle – type, route, timings, lifecycle.
Intersection – routing tables, traffic lights, queues.
TrafficLight – red/green cycles with FIFO queues.
Event – timestamped, comparable; 6 types for all DES actions.

Configuration (`simulation.properties`)

simulation.duration=60.0
simulation.arrival.model=POISSON
simulation.arrival.rate=0.5

vehicle.bike.crossingTime=1.5
vehicle.light.crossingTime=2.0
vehicle.heavy.crossingTime=4.0

statistics.update.interval=10.0

Speed logic: t_bike = 0.5×t_car, t_heavy = 2×t_car.

Topology

E1→Cr1→Cr4→Cr5→S
E2→Cr2→Cr5→S
E3→Cr3→S
Bi-dir: Cr1↔Cr2, Cr2↔Cr3

Results

Unit Tests: 7/7 ✅ 60-Second Simulation:

Generated: 22 vehicles
Completed: 5 (22.7%)
Avg system time: 15.47 s
Throughput: 0.08 veh/s
All lights & intersections operational

Performance: ~0.03 s real-time run (≈2000× speed-up), < 50 MB RAM.

Code Structure

sd/
├── engine/SimulationEngine.java
├── model/{Vehicle,Intersection,TrafficLight,Event}.java
├── util/{VehicleGenerator,StatisticsCollector}.java
└── config/SimulationConfig.java

Key Flow

Initialize intersections, lights, first events.
Process events chronologically.
Vehicles follow routes → queue → cross → exit.
Lights toggle, queues drain, stats update.
Print summary and performance metrics.

Next Steps — Phase 3

Split intersections into independent processes.
Add socket-based communication.
Run traffic lights as threads.
Enable distributed synchronization and fault handling.

TL;DR

Solid single-process DES ✅ Everything’s working — traffic lights, routing, vehicles, stats. Ready to go distributed next.

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