Traffic Control System

Context: The Arizona DOT has retained your company to diagram the functions and interactions that occur between the Control Subsystem (C) and the other 5 subsystems that make up a Traffic Signal System (TSS) at a city intersection. This baseline system architecture will then be used to expand the control subsystem capability to accommodate self-driving vehicles.

System Functionality (original design needs)

The TSS needs to control signals for intersections used by pedestrians, emergency vehicles, and personal vehicles. It also needs to monitor its own health and revert to a fail-safe operating mode when a fault is detected.

Subsystems for the Traffic Signal System (TSS)

1. Control (C)- Responsible for controlling signal sequencing based on traffic, emergency vehicle, and pedestrian information. Also, distributes power to the other subsystems
2. Lights (L)- Responsible for all controlling lights and signs.
3. Traffic Monitoring (TM)- Responsible for monitoring the volume of vehicles approaching (and waiting at) the intersection for each travel direction.
4. Emergency Vehicle (EV). Responsible for detecting emergency vehicles approaching the intersection. Reports the presence and direction of travel.
5. Pedestrian Monitoring (PM)- responsible for accepting pedestrian requests to cross. Reports request & crossing direction.
6. Health Monitoring Subsystem (HM)- responsible for monitoring system operational health and providing this information to the TCSS

System Level Use Cases

1. Commuter traffic is predominantly west during the morning rush hour. The TSS monitors the vehicle traffic density in each direction. The system adjusts the traffic signal timing to optimize throughput for westbound traffic.
2. An ambulance approaches the intersection with its warning system on. The TSS detects the approach and prioritizes the light sequence for ambulance right of way.
3. The TSS detects input from a pedestrian indicating their desire to cross the street. The system responds with appropriate traffic signal and pedestrian sign changes.
4. The system detects a fault and responds by defaulting to a fail-safe condition.

Break into Teams of 4

1. Draw the boundary for the control subsystem and list the external entities
2. Identify the needs and functions to be performed by the Control subsystem based on the system level use cases.
3. Draw the FBD for the Control subsystem