Operating speed models for heavy vehicles on tangents of two-lane rural roads

Road safety is one of the most important public health concerns in our society. In Spain, most road crashes involving heavy vehicles occur on two-lane rural roads. However, current road safety assessment procedures only rely on the analysis of the operating speed profile for passenger cars due to the few speed models available for heavy vehicles. Therefore, the main objective of this research was to analyze and model the free flow truck speeds on tangents of two-lane rural roads. To do this, the continuous speed profiles of 83 drivers travelling with their own heavy vehicle were collected by means of Global Positioning System tracking devices on 12 road sections. As a result, two different patterns were identified, which were associated with unloaded (35-54 kg/kW) and loaded (112-131 kg/kW) trucks. The most influential variables on truck speeds were tangent length, the grade of the tangent, the Curvature Change Rate of the tangent and its adjacent horizontal curves, and the speed of the preceding horizontal curve. Finally, several regression models were calibrated to predict the 85th percentile speeds for both loaded and unloaded trucks.