New Geometric Design Approach to Reduce Vehicle’s Speed in Accident-Prone Downgrade Highways Using Dynamic Vehicle Modeling

Steep downgrades are known as a part of mountain roads with a significant number of severe crashes. Generally, using speed limiters such as speed bumps and speed humps are considered the most effective (considering both the time and cost) ways to reduce the number of victims. The efficiency of speed limiters depends on the driver’s consciousness and the car’s braking system; the latter could be problematic in wet and dark conditions of the road. The main goal of the current study is to propose an approach to correct the longitudinal profile of roads by replacing the consecutive downgrades and upgrades with a continuous downgrade. The vehicle’s speed is reduced by using this method before entering an accident-prone site without the driver’s involvement and breaking. To this end, a well-known software program is used under two speeds (70 and $100\mathrm{km}/\mathrm{h}$) in 68 different routes to analyze speed along the proposed routes. Also, another computer model is used for dynamic simulation. Dynamic analyses and regression models show that the vehicle’s speed in the new proposed route is significantly reduced compared with the continuous downgrade. Moreover, results indicate that the upgrade slope of the proposed route has the most impact on reducing the final speed of the vehicles.