Probabilistic Analysis of Freeway Deceleration Speed-Change Lanes

Abstract

The design of a freeway speed-change lane (SCL) depends mainly on the manner of deceleration, initial speed, and the speed to be approached at the SCL. The design SCL length should provide drivers with sufficient distance to diverge at a reasonable speed and to decelerate comfortably. In the design guides, recommended SCL lengths are based on a deterministic approach in which a single value is assumed for each design parameter. An alternative approach is presented: a probabilistic methodology is used to analyze SCL length. This reliability-based analysis allows for the calculation of the probability of noncompliance for any specific SCL length, which corresponds to the percentage of drivers who may not be able to decelerate comfortably. Models are developed with different analysis methodologies and are applied to estimate the probability of noncompliance at seven SCL sites on the basis of speed and deceleration field data collected at these sites.