Chapter Eight - Vehicular Traffic III: Other CA Models

Abstract

The Nagel—Schreckenberg (NaSch) model is not able to capture many aspects of the fine-structure of traffic dynamics, especially the existence of metastable states or synchronized traffic. Over the recent years, a plethora of variants of the NaSch model has been proposed. This chapter discusses the most popular and successful models, which have introduced other interesting aspects into the dynamics. It demonstrates the rich variety of traffic phenomena that can be observed by appropriate modifications of the random braking, and how they lead to empirically observed metastability and the related hysteresis effects. A common feature of these models is a so-called slow-to-start rule. This refers to variants of the acceleration step, where the acceleration of standing or slow vehicles is in some sense delayed compared with that of moving cars. This can be implemented in various ways, but it will turn out that the observed behavior is rather universal. The slow-to-start rules not only lead to metastability and, consequently, hysteresis, but also to phase-separated states at high densities. They are implemented to capture the loss of attention of drivers in a jam, the slow pick-up of the motor of standing cars, and so on. Empirical evidence for the slow-to-start effect is provided.