Feasibility of the design of dual-lane ramp meters in Texas

Abstract

As recurrent congestion and the number of vehicles on urban freeways in Texas have increased, the ability to effectively meter traffic using single-lane ramp meters has deteriorated. Other state departments of transportation experiencing similar conditions have developed and implemented multi-lane ramp meters to address the increased demand volumes and variable on-ramp arrival patterns. These multi-lane systems have increased operational flexibility and available storage area compared to traditional single-lane ramp meters. The primary objective of this research was to evaluate the feasibility of designing and operating dual-lane ramp meters on frontage road/freeway slip-ramps commonly found in Texas in a safe and efficient manner. This assessment included a review and analysis of the geometric, traffic control, and operational elements necessary to operate this freeway management strategy. Based on an analysis of existing single-lane ramp meter traffic control parameters and operations, three primary evaluation criteria were established that could be used to determine the feasibility of operating a dual-lane ramp meter at a study site in Houston. These evaluation criteria included the ability to design and construct a dual-lane ramp meter on a frontage road/freeway slip-ramp configuration that adheres to the Texas Department of Transportation's engineering and safety requirements and economic considerations; the ability to meter a wide-range of on-ramp demand volumes and manage various arrival-type patterns; and the ability to contain queues within the on-ramp queue storage reservoir without spill-backs occurring on the adjacent frontage road. The conceptual dual-lane ramp meter design was examined both qualitatively and quantitatively with respect to the three established evaluation criteria. This evaluation included the analysis of the geometric design and construction evaluation, a comparative analysis of single-lane and dual-lane ramp meters, and a microscopic simulation analysis. The microscopic simulation analysis was used to compare the existing and proposed ramp meter configurations and to demonstrate the traffic control and operational flexibility of the dual-lane ramp meter design strategy. Based on these analyses and evaluations, the design and operation of a dual-lane ramp meter on a frontage road/freeway slip-ramp configuration was deemed feasible.