Design Traffic Control System
Design a Traffic Control Signal System that manages signal states at intersections.
A Traffic Control Signal System is an automated system used to manage the movement of vehicles and pedestrians at road intersections by controlling traffic lights (red, yellow, green) in a coordinated and safe manner.
Its main objectives are to:
- Regulate traffic flow by assigning right-of-way through signal phases
- Reduce congestion and waiting times at busy intersections
- Enhance safety by preventing collisions and ensuring orderly movement
In this chapter, we will explore the low-level design of a traffic control signal system in detail.
Lets start by clarifying the requirements:
1. Clarifying Requirements
Before starting the design, it's important to ask thoughtful questions to uncover hidden assumptions and better define the scope of the system.
Here is an example of how a conversation between the candidate and the interviewer might unfold:
Candidate: Should the system handle just a single intersection or manage multiple intersections concurrently?
Interviewer: It should be able to manage multiple intersections, each operating independently but centrally monitored.
Candidate: Do we need to handle emergency scenarios like green light overrides for ambulances or fire trucks?
Interviewer: Not for this version. Assume normal conditions.
Candidate: Should the system simulate real-world timing for green, yellow, and red lights?
Interviewer: Yes. Each intersection should respect configurable durations for green and yellow lights. Red is implied by the other directions being green.
Candidate: Should we monitor traffic light changes in real time?Interviewer: Yes, notify a central monitor when lights change.
After gathering the details, we can summarize the key system requirements.
1.1 Functional Requirements
- Handle multiple intersections, each operating independently
- Control signals for all four directions at a single intersection
- Support fixed configurable timing intervals for each signal phase (green, yellow, red)
- Automatically cycle through signal phases in the correct order
- Notify a central monitor when the traffic light state changes.
1.2 Non-Functional Requirements
- Modularity: The system should have clearly separated components
- Extensibility: The design should be easily extensible to support future additions
- Real-Time Responsiveness: Timing should be precise to the second, ensuring synchronization across lights
- Maintainability: The code should follow object-oriented design and be easy to update or extend
- Safety: The system must prevent conflicting signals from being active simultaneously