Investigation of side-by-side passing lane length and spacing on two-lane highways

This paper presents an investigation into passing lane length and spacing on two-lane highways. Different combinations of length and spacing were examined under various traffic levels using field data and microscopic traffic simulation. Field data from two side-by-side passing lane study sites in Oregon were used to calibrate and validate the traffic simulation program used in this study. The simulation model was then used to evaluate the effect of different passing lane length and spacing combinations on two-lane highway performance. Study results confirmed the general understanding that using longer and/or more frequent passing lanes yields better operational performance. Moreover, at higher traffic levels, a greater passing lane length, a shorter spacing or both are required to achieve the same improvement in performance. Further, results suggest that passing lane length between 0.75 and 2 miles and spacing between 5 and 15 miles provide the highest effectiveness depending on traffic level. A regression model for performance as a function of traffic flow rate, length and spacing of passing lanes was also developed.