Passenger Car and Truck Operating Speed Models on Multilane Highways with Combinations of Horizontal Curves and Steep Grades

Operating speed prediction models have been proposed as a candidate method to assess design consistency on highways and streets. A significant number of operating speed prediction models exist for passenger cars on two-lane rural highways. Few models exist for passenger cars on multilane highways, while the literature is scant for operating speed models for trucks on multilane highways. This research uses a systems modeling approach to predict passenger car and truck operating speeds on multilane highways with combinations of horizontal curves and steep vertical grades. Mean operating speeds were modeled as a function of several geometric design features and the traffic control devices present at each study site. Further, the possible endogenous relationship between passenger car and truck speeds was investigated. The findings indicate that the radius of horizontal curve appears to have a larger influence on passenger car operating speeds than truck speeds. Vertical grades appear to have a more significant influence on truck operating speeds than on passenger car speeds. Increasing the right shoulder width is associated with higher passenger car operating speeds, but the lane width was not statistically significant in the passenger car speed models. Increasing the lane width, however, was associated with higher truck operating speeds; the right shoulder width was not associated with truck operating speeds. Higher posted speed limits were associated with higher truck and passenger car operating speeds. An endogenous relationship between truck and passenger car operating speeds was found.