Modified Geometric Design Consistency Criteria for Two-Lane Rural Highways Based On Crash Severity

The present study focuses on analyzing geometric design consistency (GDC) and modifying GDC criteria and correlating them to the field-reported crash severity, specifically for heterogeneous traffic conditions on two-lane rural highways. Two National Highway (NH) sites-NH-953 (S-1, hilly terrain) and NH-56 (S-2, rolling terrain) with varying roadway conditions-were selected to achieve the study objectives. The vehicle speed data for cars and heavy commercial vehicles (HCVs) were collected using the performance box (P-Box) for the 57 curves. For the selected study curves, firstly, the GDC was analyzed using the available design consistency criteria as the difference between operating and design speed. The results indicate that the proportion of good, fair, and poor GDC for the S-1 study section are 45%, 35%, and 20% and for the S-2 study section, they are 80%, 20%, and 0%, respectively. In addition, in the S-1 study section, the vehicles (64% of cars and 40% of HCVs) and the S-2 study section (65% of cars and 0% of HCVs) moved higher than the design speed. Afterward, some modifications are made to the available design consistency criteria to establish an accurate relationship between GDC results and crash severity. The modified results revealed that fatal, grievous, and minor-injury crashes correlate well with poor, fair, and good design consistency criteria. The study results would be helpful for highway authorities to evaluate a highway's alignment consistency for its operational and safety aspects, thereby aiding some surrogate safety measures to reduce the crash probability.