Study Details
Study Title: Effect of Stopping Sight Distance on Crashes at Crest Vertical Curves on Rural Two-Lane Highways
Authors: Harwood and Bauer
Publication Date: 2015
Abstract: This paper demonstrates that the crash reduction benefits of improving stopping sight distance vary substantially over the highway system, with the greatest benefits likely to be at locations where a horizontal curve, intersection, or driveway is present in a sight-restricted area. The paper analyzes crash data for 452 crest vertical curves on two-lane highways in the State of Washington, approximately equally distributed between sites with stopping sight distance categories, but the statistical significance of these differences disappeared when a factor was introduced to account for the presence of horizontal curves, intersection, or driveways that were hidden from an approaching driver's view by the presence of the sight restriction. Instead, the presence of such hidden features was found to be highly statistically significant. There is a need for highway design guidance to give higher priority to addressing sight distance limitations where hidden roadway features are present, as well as to recognizing that sight distance improvements may have very little effect on crash frequency or severity where such hidden features are not present. Consideration should also be given to development of stopping sight distance models for use in highway design to better reflect the differences in stopping sight distance needs on various elements of the roadway system.
Study Citation: Harwood, D. and K. Bauer. "Effect of Stopping Sight Distance on Crashes at Crest Vertical Curves on Rural Two-Lane Highways." Presented at the Annual Meeting of the Transportation Research Board, Paper No. 15-3161, Washington, D.C., (2015).
CMFs Associated With This Study
Category: Alignment
Countermeasure: Presence of a horizontal curve, intersection, or driveway in a sight restricted area
| CMF | CRF(%) | Quality | Crash Type | Crash Severity | Roadway Type | Area Type |
|---|---|---|---|---|---|---|
| 1.43 | -43 |  | All | All | Not specified | Rural |
| 1.62 | -62 | | All | K,A,B,C | Not specified | Rural |
Countermeasure: Provide below criteria Stopping Sight Distance
| CMF | CRF(%) | Quality | Crash Type | Crash Severity | Roadway Type | Area Type |
|---|---|---|---|---|---|---|
| 1.22 | -22 | | All | All | Rural |
| 1.32 | -32 | | All | K,A,B,C | Rural |
