Queueing Model To Determine Variability of Recurrent Congestion at Freeway Link over a Year

Since about 1990 the quality of road traffic operation on Dutch freeways is no longer expressed as a level of service, but in the percentage of vehicles that experience congestion and in terms of their delay. The criterion for an optimal congestion percentage refers to the overall value for all working days of a year. This overall percentage is determined by means of a deterministic queueing model that simulates a year’s traffic operation. A simplified version of this model is presented in this paper. It takes into account systematic and random fluctuations in traffic demand and roadway capacity. Demand is a function of the month of the year, the day of the week, and the hour of the day, and it has a random fluctuation. Capacity changes because of light and weather conditions and also has a random component. The extent to which several sources of variation contribute to the overall percentage of vehicles experiencing congestion is analyzed as well as the total delay and the delay per vehicle involved. Moreover, the day-to-day variation of several congestion characteristics and their dependencies are discussed.