Cell transmission model (CTM) is useful for evaluating the performance of urban traffic networks due to its mathematical formalism. This paper explores the application of CTM to develop control strategies for dispersion accident-induced traffic jams and evaluates the efficiency of these strategies. On the other hand, Timed Petri nets (TPNs) perform in discrete event systems because they provide a balance between modeling power and analyzability. This paper focuses on using the developed TPNs to model variable traffic light control systems. One advantage of the proposed methods is that the traffic light behavior is clearly represented in terms of conditions and events, which result in changes in the pre-emption phase. Moreover, this paper also proposes a new control strategy to eliminate the traffic jam propagation by preventing the traffic flow heading in the direction of an accident. The analysis is performed to demonstrate how the models enforce the phase of traffic transitions by a reachability graph with time information. The liveness and reversibility of the proposed model are verified. To the best of our knowledge, this is the first paper to use TPNs to model a variable phase traffic light control system and identify its accident scenarios for the purpose of their complete avoidance. This helps the latest advanced technology in traffic safety related to the intersection of roadways.

Once a road is with a high traffic density over its loading, the traffic management has to face the fact that how to alleviate the traffic congestion and how to prevent new traffic jams from being happening in the neighbourhood. This study presents a new control strategy for alleviating the traffic congestion. For this purpose, the authors employ VISSIM to simulate and analyse of an urban traffic congestion problem. In addition, two kinds of traffic light orders are involved. On the other hand, an urban traffic network with three kinds of intersection is used to evaluate their new congestion control policy. Finally, they also demonstrate three scenario cases low, middle, and heavy traffic flow works to compare with normal regular traffic light control rules, the multiline control strategies and their new control policy. Simulation results show that their new proposed traffic control policy is the best one among the others. It is worthy of note that their new proposed policy not only alleviates successfully the congestion problem but also prevents new traffic jams from being happening in the neighbourhood.

Solving states separation problems is an important technique to obtain liveness-enforcing and optimal or near-optimal supervisors for flexible manufacturing systems based on Petri nets. It first generates the model's reachability graph and partitions it into a live zone (LZ) and a deadlock zone (DZ). Then, first-met bad markings (FBMs), which exist in DZ and are the very first entries from LZ to DZ, are forbidden by some designed place invariants (PIs) to prevent the system from entering DZ. This paper studies the reduction of the number of places to be considered in such PI designs. First, the concepts of critical transitions and critical activity places are defined, and a fast algorithm is provided to compute them. Then, the proofs of that only critical activity places need to be considered in such PI designs to forbid all FBMs and/or permit all legal markings in LZ are established.