Safety Guideline For Geometric Design Of Interstate Highway Ramp Operations

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. In contemporary China,urban road network develops rapidly, However, the corresponding design specifications can’t meet the demand for traffic safety. 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 14 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 under design speed of 60km/h, 70km/h and 80km/h. The software of UC-win/Road outputted data of vehicle’s position, steering, acceleration, speed and so on. Lateral acceleration(LA) and standard deviation of offset from road centerline(OSD) were selected as the indicators to evaluate the safety level of horizontal curve. Linear regression models quantified the correlation between drive behavior indicators and the ramp curvature. Results suggested that lateral acceleration were affected much more than the offset under design speed of 60km/h, 70km/h and 80km/h by horizontal curve radius to varying degrees. Based on the models and the previous studies, we defined threshold values for the identification of ramp circular curve characterized by “GOOD”, “FAIR”, “POOR” safety level for the ramp design speed of 60km/h, 70km/h and 80km/h. The result can provide designers with safety level information to improve the design of ramp horizontal curves.