Modelling of Operating Speed in Horizontal Alignment of Two-Lane Rural Highway

Abstract: Road accidents are most frequent and cause damage to human life and property. One of the main causes of road accidents is lack of geometric design consistency. Design consistency is defined as the relationship between the geometric characteristics of a highway which is comfortable for safe driving. The objective of this project is to develop a new operating speed model in which geometric features of alignment are considered and also to evaluate design consistency with operating speed. Geometric survey was carried out on the study stretch. Then spot speed data collection was conducted manually. From the spot speed data collected, 85th percentile speed was computed for all type of vehicles. Database include radius of curvature, curve length, deflection angle, width of road, level difference, degree of curvature, superelevation, tangent length, traffic volume, sight distance and skid number. Scatter plot was plotted to find out relationship between operating speed and various geometric parameters. Then a correlation matrix was formed from the database using the software SPSS. Significant variables found to be different for different types of vehicles. Multiple linear regression analysis was performed. Models having greater R2 value for each vehicle type were identified. Then validation was performed and selected model with least root mean square error value. Also, consistency evaluation was done based on Lamm’s criteria. Based on the criteria curves were identified as relatively good, fair and poor for all type of vehicles. This criterion makes a designer to make suitable modifications in the design from the safety point of view.

Keywords: Design consistency, Operating speed, Geometric parameters, Consistency.