Influence of Sight Distance on Crash Rates and Operating Speeds at Low-Volume Single-Lane Roundabouts in the United States

This paper seeks to investigate further the identified relationship between sight distance parameters, crash rates, and operating speeds at low-volume single-lane roundabouts in the United States. An understanding of the interaction of design, operations, and crash performance would be a step forward in the development and application of performance-based standards for roundabouts. As part of the specific objective of this paper, research was done to update and quantify further the identified relationship between crash rates, sight distance parameters, and operating speeds based on crash, traffic, and geometric data from 72 approaches to 19 single-lane roundabouts in six states. The research findings provided insight into the operational and safety effects of sight distance geometry at roundabouts. The research also identified a methodology that provided guidance for the development of performance-based standards that relied on a better understanding of those relationships. In general, the findings were consistent with previously conducted studies and indicated that exceeding sight distance thresholds increases the risk of a crash occurring. Exceeding sight distance thresholds yielded greater speed differentials between the approach and the entry to the roundabouts.