Guidelines for Right-Turn Treatments at Unsignalized Intersections and Driveways on Rural Highways

Guidelines for right-turn treatments at unsignalized intersections and driveways on rural two-lane and four-lane highways are presented. Two types of treatments, full-width lane and taper, were considered over the do-nothing radius treatment. The guidelines indicate the design hourly traffic volumes for which the benefits of right-turn treatments exceed their costs. The benefits used in the economic analysis were the operational and accident cost savings provided by right-turn treatments. The costs used in the development of the guidelines were the costs of constructing full-width right-turn lanes and tapers. The operational effects were estimated in terms of delay and excess fuel consumption experienced by through traffic due to right-turning vehicles. To account for the safety effects, the relationship between speed differential and accidents was used to estimate the reduction in right-turn, same-direction, rear-end accidents that would be expected to result from the provision of a right-turn treatment. The guidelines indicate the right-turn design hourly volume required to justify a right-turn treatment as a function of the following factors: ( a) directional design hourly volume, (b) highway operating speed, and ( c) number of lanes on the highway. Comparisons with other guidelines indicate that the range of guidelines developed are reasonable. In addition, they are more definitive than other guidelines because they account for highway operating speed and address taper treatments as well as full-width turn lanes.