Conditional free flow in U-turn segments

Abstract

Any traffic regulation scheme implemented on road systems has its limitations: it no longer functions well under certain traffic conditions. In this paper we present a phase diagram to demonstrate that in order to ensure free flow at U-turns with an on-ramp, the density of entering cars must have an upper limit. We show using spatiotemporal diagrams that the alternate density wave mechanism (between cars from the U-turn and the on-ramp) that is responsible for the dissolution of local congestion becomes insufficient above this limit creating larger traffic jams.