Analysis of Sight Distance, Crash Rate, and Operating Speed Relationships for Low-Volume Single-Lane Roundabouts in the United States.

This paper explores the relationship between sight distance parameters, crash rates, and operating speeds at low-volume single-lane roundabouts in the United States. The understanding of the interaction of design, operations, and crash performance is a step forward in the development and application of performance-based standards for roundabouts. The specific objective of this paper is to quantify the relationship between crash rates, sight distance parameters, and operating speeds to present an approach to establishing performance-based standards that highway practitioners can adopt in roundabout design. Geometric, traffic, and crash data were collected on 72 approaches to 19 low-volume single-lane roundabouts in six states. The data for these sites were broken into two groups based on the posted speed limit (at and greater than ). In addition, the associations between different sight distance parameters, crash parameters, and operating speed data were investigated. The research findings provided insight into relating the operational and safety effects of sight distance geometry at roundabouts. This research also identified a methodology that provides guidance as to the development of performance-based standards that rely on a better understanding of these relationships. In general, the research findings were consistent with previously conducted studies and indicated that exceeding sight distance thresholds increases the risk of crashes occurring. It was also found that exceeding sight distance thresholds yielded greater speed differentials between the approach and the entry to these roundabouts. The results of this research can advance the state of practice in understanding the relationships of sight distance design attributes, operational characteristics, and safety metrics for low-volume single-lane roundabouts, which is necessary to the creation of performance-based standards. [ABSTRACT FROM AUTHOR]