Validation of 1985 HCM Procedures for Capacity and LOS of Left Turn Lanes inIllinois. Final Report

摘要

The purpose of the research was to calibrate and validate the 1985 HighwayCapacity Manual procedures for capacity analysis of left turn lanes in Illinois. Saturation flow estimates for the three types of left turn treatments (Protected-only, Permissive-only and combination) were sought. In all cases, intersections with exclusive left turn lanes, fully actuated signal control and close to ideal conditions were studied. All observations were analyzed on the basis of 15-minute periods to allow comparisons between the observed data and the estimates of the HCM procedures and the prediction models developed in the study. In brief, the data analysis indicated that: (1) The ideal left turn saturation flow rate in Protected-only or Protected/Permissive phasing is 1,900 pcphgpl for Illinois traffic conditions; (2) The use of the opposing flow rate in green for estimation of left turn saturation flow and capacity is recommended both for Permissive-only and Permissive sub-phase of Protected/Permissive phasing; and (3) A combined model can be used for estimation of left turn capacity in Permissive-only and Permissive sub-phase of Protected/Permissive phasing.