Abstract: Discrete Petri nets and continuous Petri nets have their advantages and drawbacks：the former one is more accurate but more complex, while the latter one is less complex but also less accurate. As a combination of the both, hybrid Petri nets can avoid the disadvantages to some extent, and is very suitable for the modelling of traffic intersections. However, a quantitative comparison of discrete model and hybrid model is very less in previous contributions. In this paper, a top-to-bottom hybrid Petri nets modelling method for traffic intersections is proposed. Using a 4-phases intersection as example, its hybrid Petri nets model is built and compared with the pure discrete one. By simulating the system under different workload settings, it observes the queue-length of traffic flows inside intersections and discusses differences between hybrid and discrete models. To some extent, it provides the quantitative criteria of selecting an appropriate kind of model.

Key words: traffic intersection, Petri nets, modelling, simulation, comparisons

摘要： 离散Petri网和连续Petri网的各自优势和缺点明显，前者建模准确但复杂度高，后者复杂度较低但模型不够精确。混合Petri网作为两者的结合，能在一定程度上弥补各自的缺点，非常适合用于道路交叉口系统的建模。但是以往的文献中缺乏纯离散模型和混合模型之间的定量比较。提出了一种自上而下的混合Petri网方法，能够快速建立道路交叉口系统模型；以一个4相位固定相序交叉口为例，建立其混合Petri网模型并与纯离散模型进行了定量的比较与分析。通过对不同系统负载下交叉口内交通流排队长度的仿真，并考察混合模型与离散模型之间的误差变化，在一定程度上为模型选择的合理性提供了定量的依据。

关键词: 道路交叉口, Petri网, 建模, 仿真, 比较