Crash Compatibility Between Road Safety Barriers and Cars

Roadside accidents cause about one-third of the total number of traffic fatalities each year in Europe, even though roadside safety infrastructure has been developed to protect vehicle occupants. The most common countermeasures to reduce the risk of fatal and severe injuries in roadside accidents are road safety barriers. It is desirable that these structures be crash compatible with the changing fleet of vehicles to ensure consistent safety performance. An objective definition of crash compatibility was not available to assess the impact performance of cars and safety barriers. To address this, crash compatibility between safety barriers and cars was investigated by computer simulations using the finite element analysis software LS-DYNA. A W-beam guardrail system, used in Sweden as a standard roadside safety barrier, was modelled for evaluating crash compatibility. Three car models (Ford Festiva, Geo Metro and Ford Taurus) were modified to be suitable for impact analyses with the guardrail during oblique collisions. The structural configuration and geometry, of both the vehicles and roadside safety features, were identified as two primary aspects that affect crash compatibility in roadside safety, and these were studied by means of the structural surveys and parametric studies. With respect to vehicles, the dimensions, positions and stiffnesses of some car crashworthy components may significantly affect the crash consequences. A study showed that a laterally weakened car caused the impact severity of the ASI to increase by 95%. In terms of the guardrail, the global and local stiffnesses, the dimensions of the posts and the beams, and the soil embedment all affect the crash compatibility. The models developed in this work can also be used to evaluate the safety performance of the guardrail under other impact conditions. Some guidelines have been provided in the thesis, which addressed three design aspects of both vehicles and safety barriers: (1) use a structural survey as a basis for eliminating incompatible geometric configurations; (2) evaluate structural stiffnesses for eliminating incompatible stiffness properties using parametric studies; and (3) apply the criterion developed herein for evaluating crash compatibility. In future research, computer models of all common types of roadside safety features should be made and used to assess crash compatibility with the changing fleet of vehicles. Crash compatibility must be evaluated by synthesizing research on accident analysis, full-scale crash tests and computer simulations.