Design Consistency Evaluation of Two-Lane Rural Highways in Hilly Terrains

Abstract

The main objective of the geometric design consistency is to minimize the emergence of unforeseen events when road users drive along a road segment. A consistent highway design ensures that successive geometric elements act in a coordinated way. In India, vehicles with diverse static and dynamic characteristics interact with each other leading to a significant difference in traffic flow operations compared to highways in developed countries. Due to the heterogeneity in traffic flow, geometric consistency would vary significantly by vehicle category for similar curve characteristics. The present study analyzes geometric design consistency by vehicle and develops vehicle category-based design consistency models for mixed traffic environments on two-lane rural highways in hilly terrain in India. A total of 30 curves with varying geometric characteristics located along the National Highway (NH-953) connecting Netrang and Rajpipla, Gujarat, India, were selected. Speed data were collected using radar gun for three vehicles category: motorized two-wheelers (MTW), cars, and heavy commercial vehicles (HCV). Geometric design consistency was evaluated using operating speed as a surrogate safety measure. The results showed that 38% and 10% of the curves (for cars), 51% and 20% of the curves (for MTW), and 32% and 51% of the curves (for HCV) have ratings of fair and poor consistency, respectively. Design consistency models for different vehicle categories were developed using the generalized linear regression modelling (GzLM) technique. The results showed that the deflection angle is positively correlated, whereas curve and tangent lengths are negatively correlated with highway alignment design consistency.