Performance Measures on Two-Lane Highways: Survey of Practice

Two-lane highways constitute a significant component of the highway system and serve an essential function for the movement of people and goods. The Highway Capacity Manual is primarily used for operational analysis on two lane highways in the U.S., Canada and a few other countries outside North America. As part of a project sponsored by the National Cooperative Highway Research Program for improving the two-lane highway operational analysis methodology, a practice survey was conducted to gather information on agency experiences and preferences in regards to performance measurement on two-lane highways. The survey was sent to all state Departments of Transportation (DOTs) in the United States and Canada. A total of 35 usable responses were received, representing 24 states and four Canadian provinces, with a few agencies sending multiple responses. This paper summarizes the results of the agency survey and presents the most important findings. Results suggest that the top three criteria for good performance measures on two-lane highways are: sensitivity to traffic conditions, sensitivity to road conditions, and relevance to road user perception. Further, agencies identified average travel speed as the most relevant traffic flow aspect to two-lane highway operations. Other performance measures that were found meritorious were volume-to-capacity ratio and flow rate, for class I and class II highways, respectively, versus average travel speed, volume-to-capacity ratio, and percent-time-spent-following for class III highways.