How to determine Safe Speed for negotiating Horizontal Curves with Restricted Sight distance on Two-Lane Highways in India?

Abstract

Excess and inappropriate speed is a core contributory factor in road crashes. In 2018, over speeding alone has claimed the lives of 97,588 people in India, which accounts for 64.4% of the total road deaths. Horizontal curves on two-lane highways contribute to a large share of these fatalities resulting from over speeding. In general, restricted sight distance and inadequate superelevation mostly impact on the safety associated with horizontal curves. The existing geometric design guides provide deterministic design criteria for highway elements. However, in developing countries like India, due to land constraints or road encroachment, the safe sight distance is often compromised. Moreover, due to poor workmanship the superelevation and extra widening is also neglected. As a result, often the negotiating speed on a horizontal curve is not compatible and safe. Thus, in the present study, the concept of reliability was used as a tool to account for the uncertainty and evaluate the risk associated with the negotiating speed on a horizontal curve on two-lane highway. A new methodology was proposed to determine safe speed for negotiating horizontal curve under restricted sight distance for allowable maximum superelevation. The insights obtained from the study can guide practitioner in setting up competent speed limits or design effective traffic calming measures.