Study Details
Study Title: Safety Evaluation of Geometric Design Criteria: Intersection Sight Distance at Unsignalized Intersections
Authors: Himes et al.
Publication Date:JAN, 2018
Abstract: A Policy on Geometric Design of Highways and Streets, 6th Edition, published by the American Association of State Highway and Transportation Officials, provides design criteria for minimum sight distances, including intersection sight distance (ISD). An understanding of the relationship between ISD and safety at stop-controlled intersections is needed, with potential applications of this knowledge to both performance-based design and substantive road safety management practices. 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. The data were analyzed using a cross-sectional study design to quantify the relationship between safety and ISD. The analyses indicated that the expected number of target crashes are associated with available ISD. Target crash frequencies increase as available ISD decreases. Results of this research suggest that ISD is associated with expected crash frequency in a non-linear fashion. The sensitivity of the expected number of target crashes to changes in ISD is highest when ISD is shorter, and decreases as ISD increases (i.e., the safety benefit of increasing ISD from 300 to 600 feet is substantially larger than the safety benefit of increasing ISD from 1,000 to 1,300 feet). The results also suggest that the impacts of ISD on crash frequencies vary as a function of the major road two-way AADT and the major road speed limit. The sensitivity of the expected number of crashes to changes in ISD increases as both traffic volume and speed limit increase. CMFunctions for each of the target crash types were estimated using the regression models.
Study Citation: Himes, S., R. J. Porter, and K. Eccles. "Safety Evaluation of Geometric Design Criteria: Intersection Sight Distance at Unsignalized Intersections". Presented at the 97th Annual Meeting of the Transportation Research Board, Paper No. 18-05576, Washington, D.C., (2018).
Related Citations: Eccles, Kimberly, Scott Himes, Kara Peach, Frank Gross, Richard J. Porter, Timothy J. Gates, and Christopher M. Monsere. Guidance for Evaluating the Safety Impacts of Intersection Sight Distance, National Cooperative Highway Research Program, Report 875, Washington, D.C., 2018. Available at https://www.nap.edu/download/25081
Comments: The guidance and applications from this study are presented in NCHRP Report 875.
CMFs Associated With This Study
Category: Intersection geometry
Countermeasure: Change intersection sight distance
| CMF | CRF(%) | Quality | Crash Type | Crash Severity | Roadway Type | Area Type |
|---|---|---|---|---|---|---|
 |  | Other | All | All | All |
| | Other | K,A,B,C | All | All |
