Mesoscopic traffic-flow characteristics are collections of local or instantaneous vehicle movement characteristics and the characteristics derivable from them. The main ones are distributions of headway, spacing and speed. Many suitable mathematical distributions are discussed. Next, experimental examination of mesoscopic characteristics is dealt with. It was aimed mainly at comparing observed and mathematical distributions, establishing the dependence of successive values and the relationships with mesoscopic traffic flow characteristics, road characteristics and circumstances. What is known about relations between mesoscopic traffic flow characteristics and hazards is examined. As regards headway and spacing, there has been some research but it produced no results. In the case of speed, relationships have been found, showing that especially the variability around the average is important to traffic hazards. Combinations of mesoscopic characteristics are rarely related to hazards and this has not led to any results so far. Lastly, some applications of knowledge of mesoscopic traffic flow characteristics are given. They relate mainly to measures endeavouring to influence speed behaviour directly. For part I-IV see IRRD abstracts nos 240606-240609.
Abstract