Vehicle-Type and Lane–Specific Free Speed Distributions on Motorways

Abstract

A new approach to estimation of vehicle type–specific free speed distributions on multilane facilities is presented on the basis of the concept of censored observations. The original distribution-free method of Kaplan and Meier is generalized to include partially censored data, i.e., observations that are censored with a certain probability or to a certain degree. The method is applied with cross-section data collected at a busy two-lane motorway in the Netherlands. The results provide robust estimates of the speed distributions for different vehicle classes, while they remove the structural error made when more common approaches are applied.