Driver behavior and traffic flow in oversaturated intersections

Abstract

Driver behavior and traffic flow theory has been studied by researchers for decades. However, most of the studies have been aimed towards driving in undersaturated conditions. The research presented in this thesis, on the other hand, is largely directed towards driver behavior and traffic flow in oversaturated intersections. The papers describe how drivers behave in intersections with severe oversaturation, how this may be modeled, and also what can be done to relieve congestion and distribute priority in such conditions. The studies show that in unsignalized intersections, drivers cooperate in order to keep traffic moving. In the more strictly regulated environment of signalized intersections, such cooperation is only seen to a lesser extent. Two new models for cooperative behavior in unsignalized intersections have been developed and tested. The Turn Cooperation Model is a microsimulation model, included in the traffic simulation software Aimsun. The Aakre Cooperative Merge model is an analytical model. In congested situations with downstream flow restrictions, both models provide more realistic results than traditional gap acceptance models. Proposed methods for distributing priority in oversaturated intersections have also been tested through microsimulation. For signalized intersections with downstream flow restrictions, a system based on vehicle counts - rather than signal timing - is suggested. The tests support the theory that a count-based approach may provide better control of priority distribution while minimizing overall delay and aggressive driver behavior. Finally, a series of closed-track experiments with 22 drivers have been conducted, in order to obtain new knowledge on the effect of increased attention, motivation and willingness to cooperate on driver behavior and traffic flow in congested situations. In signalized and unsignalized intersections, the experiments showed that - in a test-setup - capacity gains of approximately 10-20 % may be obtained. In merge sections, the capacity increases may be even higher. Despite increased throughput, the were no indications of more unsafe situations - possibly due to the fact that the increased capacity was obtained by enhanced attention and motivation among the drivers.