Safety effects of horizontal curve and grade combinations on rural two-lane highways

2014PDFTech ReportFHWA-HRT-13-077DTFH61-11-C-00050Highway curvesHighway safetyRural highwaysTwo lane highwaysHighway gradesUpgrades (Roads)Highway factors in accidentsSafetyHorizontal curvesVertical curvesGrade interactionsCrestsSagsRural two-lane highwaysCrash modelingSafety performance functionsCrash modification factorsUnited StatesUnited States. Federal Highway Administration. Office of Safety Research and DevelopmentBauer, Karin M.Harwood, Douglas W.MRIGlobal (Firm)United States. Federal Highway Administration. Office of Safety Research and DevelopmentFederal Highway AdministrationThis report summarizes the results of research undertaken to quantify the safety effects of five types of horizontal and vertical alignment combinations for rural two-lane highways. The research is based on Federal Highway Administration Highway Safety Information System data for Washington State, including crash records from 2003 to2008. The outcome is a set of safety prediction models for fatal and injury and property damage only crashes. To present the results in a form suitable for incorporation in the American Association of State Highway and Transportation Officials Highway Safety Manual, crash modification factors representing safety performance relative to level tangents were developed from these models for each of the five combinations of horizontal and verticalalignment\u2014horizontal curves and tangents on straight grades, horizontal curves and tangents at type 1 crest vertical curves, horizontal curves and tangents at type 1 sag vertical curves, horizontal curves and tangents at type 2 crest vertical curves, and horizontal curves and tangents at type 2 sag vertical curves