Assessing Need for Systemwide Ramp Metering Installation Warrants

Abstract

Warrants for ramp metering installation have been developed by a number of U.S. states. These warrants are generally simple and are based on the traffic, geometry, and safety conditions in the immediate vicinity of each ramp (local conditions). However, advanced applications of ramp metering use system-based metering algorithms that involve metering a number of on-ramps to address system bottlenecks. These algorithms have been proved to perform better compared with local ramp metering algorithms. This situation creates a disconnect between existing agency metering warrants to install the meters and the subsequent management and operations of the ramp meters. This study focused on assessing the need for system warrants in addition to local warrants for ramp metering installation to prevent traffic breakdown at bottleneck locations. A linear programming formulation combined with consideration of the stochasticity of bottleneck capacity was used to select the ramps to be metered on the basis of the system bottlenecks. The study found that the selection of these ramps for metering—in addition to those justified by local warrants—could delay the breakdown at the system bottleneck location and improve the performance of the freeway main line. Another important benefit of selecting ramps for metering based on system operations was its distribution of on-ramp delays because of metering of more ramps and thus to a reduction in the delay experienced on the ramps selected with the existing warrants that were based on local conditions.