Study Details
Study Title: Safety Effects of Horizontal Curve and Grade Combinations on Rural Two-Lane Highways
Authors: Bauer and Harwood
Publication Date:JAN, 2014
Abstract: The safety effects of horizontal curves and grades on highways have been quantified separately, but it is not currently known whether and how the safety performance of horizontal curves and that of grades interact.
While the first edition of the AASHTO Highway Safety Manual (HSM) provides crash modification factors (CMFs) for the safety effects of horizontal curvature and percent grade on rural two-lane highways, it does not have any method for accounting for the interactions between these effects. In other words, in the HSM procedures for rural two-lane highways, the safety effect of a horizontal curve is the same whether it is located on a level roadway, a straight grade, or a vertical curve. Similarly, the safety effect of a straight grade is the same whether it is located on a tangent roadway or on a horizontal curve. Researchers have always supposed that there are interactions between the safety effects of horizontal and vertical alignment, but this has not been demonstrated in a form useful for safety prediction.
This paper summarizes the results of research undertaken to quantify the safety effects of five types of horizontal and vertical alignment combinations based on Washington Highway Safety Information System (HSIS) data and crash records from 2003 to 2008. The outcome is a set of safety prediction models for fatal-and-injury and property-damage-only (PDO) crashes. To present the results in a form suitable for incorporation in the AASHTO Highway Safety Manual, crash modification factors representing safety performance relative to level tangents were developed from these models for each of the five combinations.
Study Citation: Bauer, K.M. and D.W. Harwood., "Safety Effects of Horizontal Curve and Grade Combinations on Rural Two-Lane Highways," Federal Highway Administration, Report FHWA-HRT-13-077, January 2014.
Related Citations: Bauer, K.M. and D.W. Harwood., "Safety Effects of Horizontal Curve and Grade Combinations on Rural Two-Lane Highways." Presented at the 92nd Annual Meeting of the Transportation Research Board, Washington, D.C., Paper No. 13-3056., (2013).
Study Report: Download the Study Report Document
CMFs Associated With This Study
Category: Alignment
Countermeasure: Safety effects of horizontal curves and tangents at type 1 crest vertical curves – function for horizontal curves
| CMF | CRF(%) | Quality | Crash Type | Crash Severity | Roadway Type | Area Type |
|---|
 | |  | All | K,A,B,C | Not specified | Rural |
Countermeasure: Safety effects of horizontal curves and tangents at type 1 crest vertical curves – tangents at type 1 crests
| CMF | CRF(%) | Quality | Crash Type | Crash Severity | Roadway Type | Area Type |
|---|
| 1 | 0 | | All | K,A,B,C | Not specified | Rural |
| 1 | 0 | | All | O | Not specified | Rural |
Countermeasure: Safety effects of horizontal curves and tangents at type 1 sag vertical curves – function for horizontal curves
| CMF | CRF(%) | Quality | Crash Type | Crash Severity | Roadway Type | Area Type |
|---|
| | | All | K,A,B,C | Not specified | Rural |
Countermeasure: Safety effects of horizontal curves and tangents at type 1 sag vertical curves – function for tangents at type 1 sags
| CMF | CRF(%) | Quality | Crash Type | Crash Severity | Roadway Type | Area Type |
|---|
| | | All | K,A,B,C | Not specified | Rural |
Countermeasure: Safety effects of horizontal curves and tangents at type 2 crest vertical curves – function for horizontal curves
| CMF | CRF(%) | Quality | Crash Type | Crash Severity | Roadway Type | Area Type |
|---|
| | | All | K,A,B,C | Not specified | Rural |
Countermeasure: Safety effects of horizontal curves and tangents at type 2 crest vertical curves – tangents at type 2 crests
| CMF | CRF(%) | Quality | Crash Type | Crash Severity | Roadway Type | Area Type |
|---|
| 1 | 0 | | All | K,A,B,C | Not specified | Rural |
| 1 | 0 | | All | O | Not specified | Rural |
Countermeasure: Safety effects of horizontal curves and tangents at type 2 sag vertical curves – function for horizontal curves
| CMF | CRF(%) | Quality | Crash Type | Crash Severity | Roadway Type | Area Type |
|---|
| | | All | K,A,B,C | Not specified | Rural |
Countermeasure: Safety effects of horizontal curves and tangents at type 2 sag vertical curves – tangents at type 2 sags
| CMF | CRF(%) | Quality | Crash Type | Crash Severity | Roadway Type | Area Type |
|---|
| 1 | 0 | | All | K,A,B,C | Not specified | Rural |
| 1 | 0 | | All | O | Not specified | Rural |
Countermeasure: Safety effects of horizontal curves and tangents on straight grades – function for horizontal curves
| CMF | CRF(%) | Quality | Crash Type | Crash Severity | Roadway Type | Area Type |
|---|
| | | All | K,A,B,C | Not specified | Rural |
Countermeasure: Safety effects of horizontal curves and tangents on straight grades – function for tangents on nonlevel grades
| CMF | CRF(%) | Quality | Crash Type | Crash Severity | Roadway Type | Area Type |
|---|
| | | All | K,A,B,C | Not specified | Rural |
