3 Modeling case studies

3.2 Traffic lights¹

One kind of embedded systems are traffic lights for road crossings. Time PNs are very suitable for modeling of these. We start out with a very simple model of two crossing streets, see Figures W0 and W1. W0 shows the intersection model and in W1 a crude car model and its interaction with the lights model is shown.

Figure W0. Simple intersection model

Figure W1. Crude car-light model

We assume that the interarrival times of the cars are distributed according to the negative exponential distribution. Further we assume that the mean behaviour of the cars in passing the intersection is described by the following: for each car it takes 2 sec to react and mean time 0.5 sec (neg.exp. distribution) to pass, and the next car can only start to pass when the previous is through. These assumptions are only needed if we want to perform simulations for performance evaluation.

¹Models worked out in cooperation with Huaitien Wang from Rensselaer Polytechnic Institute, Troy, New York.