Estimating the Safety Effects of Intersection Sight Distance at Unsignalized Intersections

A gap acceptance crash is one of the most common types of multivehicle crashes at unsignalized intersections. Drivers' gap acceptance is influenced by the intersection sight distance (ISD). Before this research, the relationship between ISD and safety (measured by crash frequency) at unsignalized intersections was not quantified. To establish this relationship, crash, traffic, and geometric data were collected from 832 two-lane minor unsignalized intersection approaches in North Carolina, Ohio, and Washington State. These intersections represent a range of volumes and major road geometrics (two-lane and four-lane undivided and divided) in urban and rural areas. The sites were selected for data collection independent of historical crash frequency. The data collection included field-measured ISD using a standardized method and an exploratory measure of ISD quality. For analysis of the data, a cross-sectional study design was used to quantify the relationship between safety and ISD. The results suggest that target crashes and target fatal and injury crashes are associated with available ISD, and ISD quality is related to safety performance. Moreover, the results suggest that the impact of ISD on target crashes and target fatal and injury crashes varies as a function of the major and minor road traffic volumes.