Speed prediction models for trucks on two-lane rural highways

In the design consistency literature, the development of speed prediction models has concentrated on passenger cars, with little attention given to truck speed models. On some two-lane rural highways, however, trucks represent a large enough percentage of vehicles that they may be considered the design vehicle. The objective of the study was to develop operating speed prediction models for trucks on two-lane rural highways. A series of regression models was developed using a combination of field data and simulated data. First, the "Traffic on Rural Roads" and "Two-Lane with Passing" (TWOPAS) simulation models were critically assessed, and TWOPAS was selected to be used in further analysis. Next, field data from 17 sites were used to evaluate TWOPAS's capability in the prediction of passenger car speeds and truck speeds. On the basis of the results of this evaluation, 13 sites were selected for use in simulating truck operating speeds. These sites were used to generate additional speed data for inclusion in the database for model development. Finally, a series of regression models was developed to predict 85th percentile truck operating speeds upstream, along, and down-stream of a horizontal curve. These models consider the effect of length and grade of approach tangent, horizontal curve radius, and length and grade of departure tangent.