Evaluation of Current Design Practices for Horizontal Curves on Rural Highways Based on Vehicle Stability and Safety

Abstract: All over the world India bangs the top most position in deaths caused by road crashes. Over 1 lakh people are killed or seriously injured in road crashes in India every year, that is more than the number of people killed in all our wars put together. Sixteen children die on Indian rroads daily and there is at least one death every four minutes. Majority of the crashes are found to take place on rural highways. Rural highways are characterized by a low traffic volume and hence, speed of the vehicles is mainly controlled by the geometry. The topological conditions of India have resulted in very complex curves which include combination of horizontal curve and steep gradients up or down. In such environment, the drivers tend to choose the speeds that they perceive to be comfortable to them based on their perception of the criticality of the road geometrics ahead. Any unexpected road feature in the highway may surprise the drivers and may result in erroneous driving manoeuvres, which in turn, may end up in road crashes. As highways are meant for high speed travel, the impact of any collision that takes place will be grievous or fatal. Hence, the highways have to be designed such that their geometry directs the drivers to choose the operating speed which is in harmony with the environment.
A large number of studies are done to evaluate the effect of geometry on operating speed of rural curves. But only a few researches are done to assess the effect of geometry on the stability of vehicles. Skidding and rollover crashes are increasing dramatically, the first being more common in small vehicles like cars and the latter being more common in heavy commercial vehicles like trucks. The availability of sufficient lateral friction to counteract centrifugal force experienced by a vehicle on curve is least studied, especially in India. The values of lateral friction adopted for design of horizontal curves were developed eighty years ago by Barnett 1936; Moyer and Berry 1940. Since then, vehicle fleet has changed completely and hence the demand for lateral friction may also have changed. But the point mass equation widely used for design of horizontal curve relies on lateral friction values developed by them. Also, the equation ignores the effect of vehicular characteristics or complexity of curve geometry. So, studies focusing on revision of geometric design criteria of horizontal curves based on vehicle stability and assessment of existing margin of safety or in other words, a quantitative assessment of risk involved affecting the stability of vehicles is very important. In this paper an effort has been made to identify the gaps in current design practices and to exhibit current status of study in the field of vehicle stability on rural highways.

Keywords: Skidding, Friction, Vehicle Stability, Rollover.