Thesis (M.Eng.) - Asian Institute of Technology, 1996

A thesis submitted in partial fulfillment of the requirements for the degree of Master of Engineering, School of Civil Engineering

The study is mainly focused on the safety- effectiveness and cost-effectiveness of widening a two lane rural highway in India. Roadway width affects the occurrence of accidents. Safer roads could be achieved by sufficient road width, suitable alignment, and design of intersections. The effects of widening the pavement of a rural highway on safety, accident severity, collision types were studied in detail. Before/after analyses were carried out on accident data for 105 kms in four years. It was found that increasing number of lanes and increasing lane width and shoulder widths have improved safety and reduced accident rate by 65%. Pavement widening has reduced 60% of head on & rear end, 50% of run-off-road, 96% of pedestrian hit accidents and no effect on sideswipe accidents. The results indicate that 60% of fatalities and 70% of injuries could be reduced by roadway improvements. Models are developed to predict accident frequency in relation with layout, geometric design and traffic characteristics of one kilometer sub-sections of two-lane rural highway. A generalized linear model for accident frequency was found to provide the best fit to the data. Horizontal curvature and speed are the variables that provided the best improvement in fit and made the highest contribution to predicted accident frequency. The model could be applied to evaluate variations in accident frequency that would be associated with changes in layout, geometric design, or traffic flow on two-lane rural highways. Finally, the cost effectiveness of widening the pavement was evaluated in the sense of construction cost, reduced accident cost, travel time savings and reduced vehicle operating cost. Economic evaluation on increasing the number of lanes gives a benefit cost ratio of 2.55 a net present value of 1320 million rupees and internal rate of return of 32%. From the results, it is understood that the benefit that could be accrued from widening a pavement is two times than that of cost.