Traffic Generation for The VTI Driving Simulator

This paper describes how driving simulators are often used in a type of experiments where the result may depend on traffic conditions. One example is the evaluation of cellular phones and how they affect driving behavior. It is clear that the ability to use phones during driving depends on the amount of traffic, and that realistic experiments in driving simulators therefore must include surrounding traffic. This paper describes an ongoing project on the development of a micro simulation model for generation of stochastic traffic for the driving simulator at the Swedish National Road and Transport Research Institute (VTI). The goal is to generate a traffic stream, corresponding to a given target flow, and simulate realistic interactions in the neighborhood of the driving simulator vehicle. The model is built upon established techniques for time-driven micro simulation of traffic, where driver behavior is described by a set of fundamental sub-models for car-following, speed adaptation, lane changing etc. In this respect the model is similar to ordinary traffic simulation models, like AIMSUN (1), MITSIM (2) and VISSIM (3). A fundamental difference is, however, that, in the new model only have to consider the closest neighborhood of the driving simulator vehicle. The neighborhood can be interpreted as a window that consequently moves with the speed of the simulator vehicle. The basic purpose, and motivation for the model, is traffic generation of vehicles within sight distance of the simulator vehicle. To make this traffic realistic and to allow for speed changes of the simulator, a much wider window must be considered. The size of the window has, on the other hand, an impact on the computational time. A compromise is obtained by dividing the window into one inner and two outer regions. Close to the simulator vehicle (inner region) the “full” micro simulation model is used, while a simplified and less time consuming model is used in the two outer regions. In the latter model, vehicles are simply assumed to travel at their desired speeds. In experiments using driving simulators, a key issue is to minimize statistical variations of the result by giving all the subjects of the experiment the same conditions. With stochastic traffic different drivers will, on a micro level, experience different situations. They will soon come into new situations and interact with other traffic in a unique way. We have to accept these differences and the uncertainty that it implies, and instead say that conditions are comparable, but at a higher level. That is, each driver “feels” the same traffic flow and, in the long run, meets the same type of traffic. The first version is able to simulate traffic on a motorway with two lanes in each direction and without ramps. The paper is currently working on a rural road model, with possible overtakes and conflicts with oncoming traffic.