Modelling the Effects of Corridor Control Systems on Road Capacity

Abstract

A probabilistic description of traffic flow characteristics is given by stochastic modelling of traffic pattern generation. The basic idea is to derive a balance equation for generation and dissolution of traffic congestions. Transformed into an equation for formation of clusters consisting of jammed vehicles, this model covers traffic breakdown dynamics as a function of control parameters such as traffic volume at the beginning of the breakdown and discharge rate for congestion dissolution. From the balance equation the mean first passage time can be calculated. This time span delivers the statistics of traffic breakdowns as either a probability density distribution or as a cumulative distribution. The distributions can be used for precise definition of the road capacity connecting an observed frequency of traffic breakdowns with a probabilistic determination of the traffic perform-ance. The approach has some similarities with modelling the time to first failure in a life cycle analysis, an area where Weibull models have been widely applied. Traffic control systems with variable speed limits, keep in lane recommendations, and traffic actu-ated no passing zones - summarized as corridor control systems - affect the stability of traffic flow and directly influence the inflection point of the cumulative probability distribution for breakdowns. This influence is discussed theoretically by calculating the dependence of the probability distribu-tion with respect to the control parameters, especially with respect to the discharge rate and by ob-servation of traffic behavior with and without a corridor control system in operation. As an example several control systems on German autobahns are selected and the breakdowns are specified with respect to traffic flow characteristics at the beginning of the breakdown and the time duration of the breakdown. Based on the average daily traffic volume, the analysis enables traffic engineers and road designers to decide whether a corridor control system is worth installing or whether other traffic relief meas-ures should be applied such as improved incident management and higher service patrol density.