Traffic Light Model

As anyone who lives in Potsdam knows, traffic lights can be very complex
systems.  The best way to model a traffic light is to start with a simple system
and then gradually add to it as you debug it.

The simplest system would have four lights, N, S, E, W, which each have three
states, R, Y, G, and would operate synchronously. You would add other components
such as sensors under the road and pedestrian crossing buttons, which would
modify the behavior of the lights.

You would also have to think about what specs your system should satisfy and
how to formalize them in Alloy or NuSMV.