Study designs for passing sight distance requirements

This report documents the results of an examination of the passing sight distance standards in A Policy on Geometric Design of Highways and Streets, published by the American Association of State Highway and Transportation Officials (AASHTO), and the current sight distance requirements for marking passing and no-passing zones cited in the Manual on Uniform Traffic Control Devices (MUTCD). Relevant findings in the available literature are summarized. The current AASHTO design standards and MUTCD marking standards related to passing sight distance on two-lane highways are described. Issues related to the current standards and practices are identified and discussed. This includes the results of a meeting of knowledgeable authorities. Finally, three experimental plans that address three selected, critical issues are presented. These include (1) an accident-based analysis of current practices, (2) a field-based observational study of passing behavior to determine the adequacy of the current standards, and (3) a field-based observational study of passing behavior to determine if the minimum passing zone length of 400 ft (122 m) implied in the MUTCD is inadequate and to determine what the minimum passing zone length should be. These three plans may serve as a basis for future research.