Effect of Shoulder on Safety of Highways in Horizontal Curves Using Vehicle Dynamic Modeling Considering Yaw Rate

Document Type : Research Article

Authors

1 Department of Civil Engineering, K. N. Toosi University of Technology, Tehran, Iran

2 Department of Civil Engineering, Imam Khomeini International University (IKIU), Iran

3 Civil Engineering Department, Imam Khomeini International University, Qazvin, Iran

4 Expert engineer at Ministry of Energy, Tehran, Islamic Republic of Iran

5 Technical and Soil Mechanics Lab.co, Ministry of Roads and Urban Development

Abstract

Skidding in horizontal curves is a common type of accident that endangers passenger safety and may happen due to various reasons. Investigating the co-relations between Vehicle dynamic parameters and road shoulder type by taking yaw rate changes, the human factor (speed and encroachment angle), and road geometry (width, material, and slope of shoulder and roadway) via vehicle dynamic simulation helps to realize the skidding mechanism on horizontal curves caused by the shoulders. The importance of this study reveals by considering that similar studies have not probed the relations between vehicle dynamic and shoulder parameters based on observing the danger of skidding. The simulation process in this study is conducted via the vehicle dynamic simulation software Carsim and Trucksim which can evaluate the stability of the vehicle in various driving conditions. By conducting 324 scenarios generated by the simulation software, several models are achieved based on the relation between parameters affecting vehicle yaw rate for Sedan, SUV, and Truck types of vehicles. Scenarios are generated by considering unwanted road departures in horizontal curves in all types of vehicles with various speeds and placements of outer tires on different types of shoulders. As the results of the simulated scenarios demonstrate, the average yaw rate of a Truck is 6.41 to 19.65 percent higher than the SUV and Sedan types, respectively. Even though the average amount of yaw rate for Sedan against SUV and Truck is greater by 6.7% and 20%, respectively. Also, the simulation results show that when the outer tires are on a gravel shoulder and the inner ones are on the roadway in horizontal curves, the amount of yaw rate for Sedan, SUV, and Truck would be 1.06, 0.76, and 0.66 percent, respectively, which are lower than the cases in which the gravel shoulder is replaced with an asphalt one. Furthermore, Results indicate that shoulders with various widths, cross slopes, and materials, influence aspects of highway safety-related to vehicle yaw rate significantly. This influence depends on the dynamic and geometric features of each type of vehicle.

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