Effect of the tangent element of horizontal alignment on driving speed on two-lane rural roads

Abstract

The lack of coordination between adjacent geometric elements of horizontal alignment can lead to unsafe speed. This paper presents a study on driving speed at tangents on the regional roads. This study evaluated the effect of tangent and adjacent elements of horizontal alignment on driving speed distribution for two-lane rural roads and developed prediction models for operating speed. Spot speed data of vehicles were analysed at 500 road sections. Statistical analysis of the speed data of 300 sites revealed a critical vehicle category. The effect of preceding elements and tangent length on driving speed were analysed, and the critical length of tangent was identified as the most influencing parameter. An operating speed prediction model (OSPM) for tangent was developed using regression analysis. The proposed OSPM was compared to the models developed by various authors; and the related design consistency and traffic safety issues were discussed. The results are expected to benefit both other researchers and the organisations responsible for the development and implementation of normative technical documents for road design.