Speed prediction models for trucks on horizontal curves of Spanish two-lane rural roads

Road safety is closely related to geometric design consistency, which is usually assessed by examining operating speed. Most of consistency models only consider passenger car speeds, even though the interaction between passenger cars and heavy vehicles plays a pivotal role on road safety. This is due to the few models to estimate heavy vehicle speeds. This study aims to develop speed prediction models for heavy vehicles on horizontal curves of two-lane rural roads. To do this, continuous speed profiles were collected by using Global Positioning System (GPS) tracking devices on eleven road sections. As a result, truck speeds were analyzed on 105 horizontal curves. The results showed that the radius of the horizontal curve and the grade at the point of curvature have a great influence on heavy vehicle speeds. To this regard, vertical alignment only has a significant effect on truck speeds developed along upgrades. In addition, different trends were identified for loaded and unloaded trucks. Several speed models were calibrated for both loaded and unloaded trucks. As a result, heavy vehicle speeds were adversely affected by grades greater than 3%. This phenomenon was larger for loaded trucks than for unloaded ones. Finally, the calibrated 85th and 15th percentile speed models were compared with those developed previously. As a conclusion, the use of the proposed models in this study was recommended on Spanish two-lane rural roads due mainly to the different characteristics of heavy vehicles around the world.