Abstract—Emergency vehicles (EVs) play an important role in public service. And the EV’s timeliness and safety are very important. Focusing on the switch of the phases in a four-phase intersection, this paper presents a novel phase-changing model based on timed Petri nets (TPNs) for the traffic light system and proposes a method that uses TPNs to model the preemption of emergency vehicles in such an intersection. Our model ignores many actual details. By controlling the phases, our method ensures that the EVs can pass through the intersection with no or less delay, and the safety of the traffic model on emergency scene can be ensured. To our knowledge, we are the first to employ TPNs to model EV system on a four-phase intersection. The liveness and reversibility of such a TPN model are also verified through the reachability graph of the TPN.