Several models have been developed to determine the minimum passing sight distance (PSD) required for safe and efficient operation on two-lane highways. The American Association of State Highway and Transportation Officials (AASHTO) has developed a model assuming that once the driver begins a pass, he/she has no opportunity but to complete it. This assumption is believed to result in exaggerated PSD requirements. Considerably shorter PSD values are presented in the Manual on Uniform Traffic Control Devices (MUTCD) and are used as the marking standards in Canada and the USA. However, the reasons for selecting these values are not stated. More appropriate models have been developed considering the driver's opportunity to abort the pass, and a critical sight distance is determined. The critical sight distance produces the same factor of safety whether the pass is completed or aborted. However, these models need to be revised to determine the PSD requirements more accurately and to closely match field observations. In this paper, a revised PSD model is used to develop design values for the minimum required PSD and is extended to determine the minimum length of passing zones and the profile of required PSD along the entire pass. The results show that the PSD requirements and minimum lengths of passing zones recommended in the MUTCD are sufficient for low speeds only. For design speeds higher than 70 kph, the deficiency in the MUTCD requirements increases with the increase in the design speed and subsequently the increase in the severity of potential collisions. Although the minimum lengths of passing zones used in Ontario are reasonable for passing maneuvers involving passenger cars, major revisions to the current MUTCD marking standards are needed.
Samenvatting