This paper reports a study of the flow and safety benefits of paved shoulders on heavily trafficked two-lane rural roads, at ten sites in northern Israel. The first part of the study comprised theoretical analyses of the increases in speed and total throughput capacity (lanes and shoulders) of roadway sections. Significant increases in both speed and throughput capacity were found. A model was developed for the impact of the use of shoulders by slow-moving vehicles on the highway flow. In the second part of the study, an analysis of speed data and accident rates was conducted for sections where the shoulders had been recently paved. It was found that speeds increased, although not substantially, and that accident rates were reduced at 70 percent of the sites studied. In the third part of the study, threshold volume-to-capacity ratios (v/c) were developed for sections with different slopes and truck percentages. The v/c ratios, above which paving of shoulders on two-lane rural highways was justified on the basis of a reduction in average delay, ranged from 0.54 to 0.66. The observed roadway sections ranged from level terrain carrying 5 percent trucks to a 7 percent slope with 20 percent trucks. Further research is suggested, particularly a cost-benefit analysis of paved shoulders. (a).
Abstract