IMPACT OF PASSING LANES ON THE QUALITY OF SERVICE ON TWO-LANE HIGHWAYS

Two main procedures have been used to determine the impact of passing lanes on the quality of service on two-lane highways in Canada. One procedure has been the use of the Australia Road Research Board TRARR two-lane highway simulation model. The second procedure, which is the focus of this paper, is the use of mathematical models based on the passing opportunities concept. These models have been developed to provide a more realistic measure of level of service as perceived by the motorist, as well as a procedure which could be used at the preliminary planning state of determining if passing lanes are warranted. Three Canadian highway agencies have developed their own particular version of the passing opportunity concept. The passing opportunity models allow the analyst to determine the reduction in percent following for a given volume, directional split, percent of passing lanes for a given length of two-lane highway in level, rolling, and mountainous terrain. In summary, the main purpose of passing lane analysis using a simulation model such as TRARR is warranted. While mathematical models based on overtaking supply and demand provide a better representation of drivers perceptions of quality of service than traditional measures based on volume/capacity ratios, their limitations in terms of simplifying assumptions are noted in the paper.