A study of traffic performance and design of passing lanes on two-lane, two-way rural highways emphasised four major research areas.Field studies of traffic performance and design of five california passing lanes provided an operational assessment and focused attention on the other three research efforts. A before-and-after field study of two passing-lane entrance designs demonstrated that the modified design significantly increased the proportion of traffic that would enter the passing-lane section in the basic lane. Field observations of passing manoeuvres clearly indicated that the number of passes per passing-lane length was a good measure of effectiveness of passing lanes. Equations were developed for estimating the number of passes as a function of traffic flow level for each of the five data sets. A sensitivity analysis through simulation identified that passing lanes from 0.25 to 0.75 mi long appeared to be the most effective and that spacing of 2 to 5 mi between such passing lanes appeared appropriate depending on downstream roadway and traffic conditions. The number of passes that would likely occur at three of the field sites under various traffic flow levels and vehicle composition mixes was estimated.
Abstract