Operating Speed Prediction on Crest Vertical Curves of Rural Two-Lane Highways in Nebraska

Abstract

Since the repeal of the National Maximum Speed Limit by the U.S. Congress, individual states have been modifying existing speed limits on state and federal highways. Increases in speed limits have caused the inferred design speeds of many crest vertical curves along two-lane rural highways to be less than the posted and operating speeds according to accepted national guidelines. Past research has found that rate of curvature and inferred design speed can be used to predict operating speeds on crest vertical curves. Crest vertical curve, roadway, traffic, and speed characteristic data are included to determine the features that influence the speeds on crest vertical curves. Speed data were collected on 70 crest vertical curves across Nebraska. Multiple linear regressions were included to determine the crest vertical curve, roadway, traffic, and speed characteristics that affect speeds on crest vertical curvature. The posted speed of the highway was found to have the most influence on the operating speed. The inferred design speed of the vertical curves was not a significant factor.