At head of title: National Cooperative Highway Research Program.

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 (i) 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.

The progress that has been made in developing the positive guidance concept is documented, and the meaning of positive guidance, the philosophy of driver performance upon which it is based the nature of the driving task at those locations where positive guidance is applicable, and a procedure for its application are discussed. This report describes what must be done to improve the information system at hazardous locations. Positive guidance which is an information system matched to the facility characteristics and driver attributes, is based on the premise that a driver can be given sufficient information where he needs it and in the form that he can best use to avoid hazards.

Sight distance is an important consideration in roadway design, affecting many aspects of highway safety and operations. Ramp, interchange, and intersection designs are typically completed in tightly constrained spaces with many structural, earthwork, and roadway features present that may obstruct sight distance. These features are not easily moved; if consideration of sight distance constraints is not given early in the design process, designs may be compromised and a reduced level of safety may be encountered by the public on the completed roadway. After conducting a literature review of design criteria, three case studies of interchange ramps, and a thorough review of the TxDOT Design Division Operations and Procedures Manual, recommended revisions were prepared for the manual. These revisions include material intended to clarify and extend the consideration of sight distance in roadway design.