| The preferred design for intersections includes adjacent legs that intersect at 90 degrees. However, there are occasions where physical constraints result in intersection angles less than 90 degrees, and thus produce skewed intersections. Such intersections create potential safety and operational problems for both motorists and non-motorists. To date, the research on such issues 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, where safety is defined by intersection crashes. The relationships were used to 1) determine appropriate crash modification factors for reducing or eliminating the skew angle of an intersection, 2) determine if there is a critical minimum angle at which safety is substantially diminished, and 3) assess the need for revision of current geometric design policies and practices.;The data for this research were acquired from the Federal Highway Administration Highway Safety Information System and the Minnesota Department of Transportation. A supplemental data collection effort was undertaken to acquire additional key variables, including all measured angles at each intersection. The final database of minor leg stop-control intersections included 1,669 4-leg locations and 1,109 3-leg locations. The numbers of crashes included in the analysis over a 7-year period were 8,482 and 4,746 for 4-leg and 3-leg intersections, respectively.;Data mining techniques were used to identify the most important predictor variables from a large list of independent variables. Negative binomial regression models were then developed using the identified variables. The models with the best fit were used to derive crash modification functions (CMFs) for 3-leg and 4-leg intersections separately. The shape of the relationship between CMF value and intersection angle differs from prior CMFs developed. It is also recommended that the minimum critical angle for intersections in roadway design policies be revised to 75 degrees. The results may change the way road safety professionals make decisions regarding improvements to skewed intersections. |
