Multivariate Operating Speed Forecasting Model Based on the Geometric Elements of Two-Lane Highways

Abstract

Operating speed forecasting models for two-lane highways have been used since the mid 1950s. Most of those models use the radius of curvature as the only independent variable. Although models that attempt to include other important geometric elements (longitudinal grade, curve side, road width, etc.) present higher coefficients of determination (R2), most times they turn out not to be statistically valid. That fact results from the correlation between the geometric variables of the design stage, characterizing their classification as independent variables and inflating the model. The use of multivariate analysis, using principal components allows the transformation of the geometric variables into orthogonal components in relation to each other, i.e., independent from each other. Using this tool, this paper presents an operating speed forecasting model using the geometric elements (radius, curve side, longitudinal grade) for two-lane highways in Brazil. The paper also presents a sensitivity analysis of the proposed model. 