Optimized design of roadside trees based on the risk analysis of occupant injuries in traffic accidents

To reduce occupant injuries in collisions between vehicles and roadside trees, this paper introduces the acceleration severity index (ASI) as an indicator of occupant injury risks and uses the vehicle dynamics simulation software PC-crash to carry out offset crash tests of vehicles and trees along the roadside. The recommended diameter of roadside trees with the minimum ASI is given by collecting various ASI data corresponding to different vehicle departure speeds and slope gradients, and the multivariate models of vehicle departure speeds, slope gradients and diameters of roadside trees, as well as the minimum ASI, are fitted. In the case of the minimum ASI >1, by further adjustment of the diameter of roadside trees, the calculation method of the distance to trees is proposed, and the optimized design schemes of the roadside tree diameter and spacing with the minimum ASI ≤1 for different vehicle departure speeds and slope gradients are given. The results show that the vehicle departure speed is positively logarithmic to the recommended diameter of roadside trees and is positively exponential to the minimum ASI. The slope gradients are approximately positively linearly correlated with the tree recommended diameter and minimum ASI. When the slope gradients are 1:6.5~1:3.5 with a vehicle departure speed of 100 km/h~120 km/h, when the slope gradients are 1:2.5 with a vehicle departure speed of 90 km/h~120 km/h, and when the slope gradients are 1:1.5 with a vehicle departure speed of 80 km/h~120 km/h, the corresponding minimum ASI >1, which indicates that the severity of roadside accidents exceeds the limit that an occupant can endure.