A microscopic investigation into capacity drop: impacts of a bunded acceleration and reaction time

Abstract

Capacity drop indicates that the queue discharge rate is lower than the road capacity. Due to the capacity drop, traffic delays increase once queues form. Researchers find that queue discharge rates vary in different traffic conditions. Empirical data shows that the queue discharge rate increases as the speed in congestion increases. Understanding what and how driver behaviors result in such variable queue discharge rates can help minimize traffic delays and eliminate congestion. However, as far as authors know, few efforts have been devoted to testing impacts of traffic behaviors on the variable queue discharge rate. This paper tries to fill in the gap. The authors investigate to what extent acceleration variety and reaction time can influence the queue discharge rate. It is found that the acceleration variety cannot reduce the queue discharge rate considerably. Modelling reaction time might be more important than modeling acceleration when giving capacity drop in car-following models. A multi-phase reaction time mechanism for giving variable queue discharge rates is proposed. That is, decreasing reaction time as the speed in congestion increases can give the same variable queue discharge rate as empirical observations. The research might indicate that motivating drivers to speed up earlier could benefit increasing queue discharge rates and minimizing delays.