Evaluation of design consistency methods for two-lane rural highways : executive summary

008196342000PDFResearch PaperFHWA-RD-99-173Highway designGeometric designComputer modelsDesign speedSpeed distributionComputer aided designRural highwaysTwo lane highwaysSpeed limitsHighway planningHighway safetyDesign consistency, Interactive Highway Safety Design Model (IHSDM)Driver workloadHighway geometric design consistency evaluation methodsSpeed predictionSpeed profileUnited States. Federal Highway AdministrationFitzpatrick, KayTexas Transportation InstituteNTL-HIGHWAY/ROAD TRANSPORTATION-HIGHWAY/ROAD TRANSPORTATIONNTL-HIGHWAY/ROAD TRANSPORTATION-DesignNTL-SAFETY AND SECURITY-Human FactorsNTL-SAFETY AND SECURITY-Speed LimitsNTL-SAFETY AND SECURITY-Highway SafetyNTL-OPERATIONS AND TRAFFIC CONTROLS-Traffic FlowFederal Highway AdministrationDesign consistency refers to the conformance of a highway's geometry with driver expectancy. Techniques to evaluate the consistency of a design documented within this report include speed-profile model, alignment indices, speed distribution measures, and driver workload. The use of operating speed as a consistency tool requires the ability to accurately predict speeds as a function of the roadway geometry. In this research project, several efforts were undertaken to predict operating speed for different conditions such as on horizontal, vertical, and combined curves; on tangent sections using alignment indices; on grades using the TWOPAS model; and prior to or after a horizontal curve. The findings from the different efforts were incorporated into a speed-profile model. Alignment indices are quantitative measures of the general character of a roadway segment's alignment. These potential indicators may identify a geometric inconsistency when there is a large increase in the magnitude of the alignment indices for a successive roadway segment or feature or when a high rate of change occurs over some roadway length. Speed distribution measures investigated included variance, standard deviation, coefficient of variation, and coefficient of skewness. Driver workload is a measure of the information processing demands imposed by roadway geometry on a driver. Principal investigators were Kay Fitzpatrick and Raymond A. Krammes with with contributions by (in alphabetical order): Ingrid B. Anderson, Karin M. Bauer, Jon M. Collins, Lily Elefteriadou, Paul Green, Douglas W. Harwood, Nelson Irizarry, Rodger Koppa, John McFadden, Kelly D. Parma, Karl Passetti, Brian Poggioli, Omer Tsimhoni, and Mark D. Wooldridge. Work performed under contract DTFH61-95-R-00084. 9 Figures, 5 tables, 13 references. 384k, 29p