Impact of On-Ramp Traffic Flow Arrival Profile on Queue Length at Metered On-Ramps

Abstract

At a metered on-ramp, a vehicle queue will be formed in front of the ramp meter when on-ramp demand exceeds the ramp-metering capacity. It is therefore important to provide adequate queue storage space to prevent ramp queue from spilling to the upstream feeding facility, particularly when a metered on-ramp is retrofitted to an existing unmetered ramp. This paper investigates the impact of on-ramp traffic flow arrival profile on queue length at four metered on-ramp types. Based on field investigations at 13 ramp-metering locations, it was found that a higher demand-to-capacity ratio might not automatically lead to more queue storage needs; this nonlinear relationship indicated that queue length tends to be affected by the stochastic nature of on-ramp traffic flow. An analytical approach was then employed to model the on-ramp traffic flow arrival profile at each metered on-ramp type; results revealed that the on-ramp traffic flow arrival profile affected the queuing process at metered on-ramps. Finally, the microsimulation method was used to simulate queue lengths under various demand-to-capacity ratio scenarios at each metered on-ramp type. It was found that the queue generated by the random on-ramp traffic flow arrival profile at Type 4 metered on-ramps was up to 30% shorter than the queue generated by the nonrandom on-ramp traffic flow arrival profiles at Types 1, 2, and 3 metered on-ramps. The platoon dispersion effect at Type 3 metered on-ramps reduced queue length by up to 19.6% in comparison with Type 1 metered on-ramps; simulated queue length at Type 2 metered on-ramps was found to be 5.3% shorter than at Type 1 metered on-ramps.