OPTIMAL DESIGN OF HIGHWAY CRASH CUSHIONS

Abstract

Crash cushions are deployed at gores and in front of other fixed objects along the roadway when their proximity to the travelled way poses an unacceptable risk to the travelling public. A crash cushion is intended to act as a deformable shield that causes an errant vehicle to decelerate more slowly, dramatically reducing the potential severity of injuries suffered by vehicle occupants. This paper formulates the design of such a system as a constrained optimization problem which is solved using contemporary search techniques implemented in commercial software. The methodology is demonstrated on high-molecular-weight, high-density polyethylene (HMW/HDPE) cylinders arrayed in a single line to form a crash cushion which carries the trade name REACT® 350 system. The wall thickness of each cylinder in the array is treated as a design variable. The diameter of the cylinders and the total number in the array are treated as parameters and not directly addressed by the optimization process. A simple one dimensional array of masses and nonlinear springs are used to simulate the dynamic interaction of a vehicle and the cushion system and yield a value for the Occupant Impact Velocity (OVI) and Ride Down Acceleration (RDA) for a given set of cylinder parameters. Prescribed upper limits on OVI and RDA under impact of two standard mass vehicles form the four implicit, nonlinear constraints in the problem. The objective function to be minimized is the total weight of the barrels used over all cylinders in the system. Optimization results are presented for one REACT® system reported in the literature.