Real-time route diversion control at congested freeway off-ramp areas

Abstract

This paper develops, investigates and demonstrates real-time route diversion policies in cases where recurrent freeway traffic congestion is created due to a saturated off-ramp. In particular, the proposed route diversion policies attempt to avoid the off-ramp queue spill-over onto the freeway mainstream and the resulting freeway congestion by appropriately re-routing the freeway vehicles through nearby off-ramps towards the same destination. The proposed route diversion concepts are based on feedback control laws and are tested for a hypothetical, but quite typical, network infrastructure and three different traffic scenarios by use of macroscopic simulation. In the first traffic scenario, the user-optimal conditions may be achieved without off-ramp queue spill-over and creation of mainstream congestion; thus the route guidance system may propose an alternative route without any disbenefit for the compliant drivers. In the second case, the user-optimal conditions may be achieved only after the off-ramp queue spills back to the mainstream freeway; thus the route diversion system will have to assume sufficient compliance to the proposed route choice; or be based on mandatory actions, such as temporary off-ramp closures. Finally, in the third examined case, the user-optimal conditions cannot be achieved, due to the traffic conditions on the alternative route, thus the route diversion system should decide for the temporary off-ramp closure, when and to the extent needed, in order to prevent formation of mainstream congestion. The obtained simulation results are compared to the case where no route guidance is applied to the network and reveal interesting features and the potential for significant improvements.