A speed-profile model for estimating 85th percentile speeds along horizontal alignments of rural two-lane highways in the United States is documented. The model is an evaluation tool to check for speed consistency violations on alignments with design speeds less than 100 km/h (62.1 mph). The model was calibrated by using speed and geometry data collected for 138 horizontal curves and 78 approach tangents on 29 rural highways in 5 states. A preliminary evaluation suggests that the model provides reasonable estimates of the reductions in 85th percentile speeds from an approach tangent to a horizontal curve.
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