SD/STEP2_SUMMARY.md

🏁 Single-Process Prototype — Implementation Summary

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

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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.

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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.

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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.

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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.

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Topology

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

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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.

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Code Structure

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

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Key Flow

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

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Next Steps — Phase 3

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

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TL;DR

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