Impact of Intersection Angle on Highway Safety

FHWA-HRT-20-067

Impact of Intersection Angle on Highway Safety

David Harkey, Bo Lan (ORCID: 0000-0002-7998-7252), Raghavan Srinivasan (ORCID: 0000-0002-3097-5154), Wesley Kumfer (ORCID:0000-0002-6705-5298), Daniel Carter (ORCID: 0000-0001-6572-6548), and Anusha Patel Nujjetty (ORCID: 0000-0002-1148-718X)

Highway Safety Research Center
University of North Carolina
Chapel Hill, NC 27599

Office of Safety Research and Development
Federal Highway Administration
6300 Georgetown Pike
McLean, VA 22101

This report was produced as a research product of the Highway Safety Information System (HSIS) under the direction of HSIS Program Managers Carol Tan, Ph.D. (HRDS-20; ORCID 0000-0002-0549-9782) and Ana Maria Eigen, Ph.D. (HRDS-20; ORCID 0000-0003-4056-361X).

The preferred design for conventional intersections includes adjacent legs that intersect at 90 degrees. However, there are occasions when physical constraints result in intersection angles less than 90 degrees and thus produce skewed intersections. Skewed intersections may create potential safety and operational problems for both motorists and nonmotorists. To date, the research on problems related to skewed intersections has been limited, which may explain the lack of consensus among the policies and guidance that now exists in practice. The objective of this study was to derive quantitative relationships between intersection angle and safety for which intersection crashes define safety. The relationships were used to determine appropriate crash modification functions (CMFunction) for reducing or eliminating the skew angle of an intersection, determine if there is a critical minimum angle at which safety is substantially diminished, and assess the need for revising current geometric design policies and practices.
Data-mining and -regression techniques were used to identify the most important predictor variables from many independent variables. Data from minor road stop-controlled intersections in Minnesota and Ohio were used to estimate negative binomial regression models using the identified variables. These models were used to derive CMFunctions for rural and urban three- and four-leg intersections. The relationship between the crash modification factor and intersection angle (represented by the CMFunctions) differs from previous studies. Agencies should consider modifying the minimum critical angle for intersections in roadway design policies to be revised to reflect the results of this research.

Intersection angle, intersection safety, crash modification factor, crash modification function, skew angle, negative binomial regression, stop controlled

Unclassified