Design Consistency Evaluation Tools for Rural Highways: A Review

Rural highway safety and efficient driver performance are usually associated with consistent highway geometric design. Inconsistency in the rural highway design is determined to be the primary cause of single-vehicle crashes at curve sites. The primary objective of the current review article is to summarize the various tools and their threshold values used in the literature and to discuss the various tools that evaluate the consistency of rural highways. Twenty-nine research articles along with a geometric design code were selected according to eligibility criteria. The eligibility for research articles was that they must include at least one consistency tool, consistency process, assumption of free flow condition and consistency evaluation must be on rural highways. The evaluation process is defined under four consistency measures: speed consistency, dynamic consistency, alignment consistency, and consistency through the driver’s workload. The study found that most of the consistency evaluation tools are developed based on the speed and geometric data of two-lane rural highways. Speed consistency is found mostly explored measure since over-speeding is the prime reason for the single-vehicle crash. Moreover, input parameters were selected for consistency evaluation primarily based on the vehicle, road, and driver’s characteristics such as speed, road geometry, and visual demand respectively. Roadside environmental factors, driver’s real-time perception, and vehicle dynamic advancement are rarely explored to assess consistency.