Modeling the Effects of Driver and Road Geometric Characteristics on Consecutive Horizontal Curve Perception

Driver errors are the major contributors to run-off-road crashes on horizontal curves. Hence, understanding driver perception of horizontal curves is essential for improving road safety. This study examined the combined effects of driver characteristics such as, age, driving experience, annual distance driven, driver type, education, eyeglass use, and geometric features such as radius of preceding curve ( R P ), difference between radii of preceding and succedding curves (Δ R ), deflection angle ( DA ) on consecutive horizontal curve perception. A questionnaire survey was conducted using simulated images of various curve combinations of four-lane rural highways. Ninety-five male drivers examined the images for differences between consecutive curves and responded in a dichotomous (Yes/No) format. Preliminary analysis identified no significant relationship between driver responses and operating speed. Additionally, image- and video-based presentation methods for examining consecutive curve perceptions were found to be statistically comparable. Driver responses were modeled using mixed-effects logistic regression, identifying ΔR , R P , Annual distance driven × ΔR , Annual distance driven × DA , and Driving experience × ΔR as significant predictors. The developed model evaluates geometric consistency based on the probability of correctly perceiving curve differences. For existing alignments, curve combinations with R P = 300-400 m and Δ R = 50–150 m (e.g., threshold probability < 0.5) were deemed perceptually inconsistent and recommended for treatments like speed signage or chevron signs. For new designs, combinations with R P = 150–300 m, Δ R = 150–300 m, and DA = 30–90 degrees were identified as perceptually consistent. The findings support safety policy recommendations, including graduated driver licensing for drivers with ≤10 years of experience and supervised training for drivers covering ≤1,000km annually.