Role of vehicle trajectory and lateral acceleration in designing horizontal curve radius of off-ramp: a driving simulator based study

Freeway ramp areas are usually considered to be the most dangerous areas of freeways, where frequency of severe crashes is much higher than other freeway segment. However, few studies transcend traditional boundaries and shed some light on the design of ramp highway horizontal curves in view of driver behavior. The overall objective of the research was to find the correlation between horizontal curve radius and ramp safety using a driving simulator equipped with the software of UC-win/Road. To realize this objective, freeway off-ramps with 8 different scenarios of horizontal curves were modeled strictly geo-based on Shanxi’s design blueprints on the driving simulator and twenty volunteers were recruited to drive on it. The software of UC-win/Road outputted data of vehicle’s position, steering, acceleration, speed and so on. Lateral acceleration (LA) and offset from road centerline were selected as the indicators to evaluate the safety level of horizontal curve. Linear regression models quantified the correlation between drive behavior elements and the ramp curvature. Results suggested that offset and lateral acceleration were affected by horizontal curve radius to varying degrees. Based on the models and the previous studies, we provided the quantitative lower and upper bounds of radius. The results are promising and further analysis will provide recommendations for updating the design of ramp horizontal curves.