Road safety is one of the most important public health concern in our society. In Spain, the most of the traffic accidents involving a heavy vehicle occur on two-lane rural roads. Current consistency models 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 speed developed by heavy vehicles on tangents of two-lane rural roads. Thus, this research presents new speed models for estimating heavy vehicle speeds on tangents of two-lane rural roads. To do this, truck speeds were collected by means of Global Positioning System tracking devices, on 49 tangents sections that were identified from 12 road sections. Two different patterns were detected, which were associated with loaded and unloaded trucks. The combined effect of geometric and operational variables was analyzed. As a result, the most influential variables on loaded truck speeds were the speed of the preceding horizontal curve and the grade of the tangent, whereas unloaded truck speeds were significantly influenced by the length of the tangent and the speed of the preceding horizontal curve. Finally, several regression models were calibrated to predict the 85th and 15th percentile speeds for both loaded and unloaded trucks.