As new passenger rail cars are introduced into existing rail fleets, the potential structural for incompatibility between cars in a collision is a safety concern. Crush damage that occurs when dissimilar strength vehicles collide is concentrated in the weaker vehicle. In a serious collision the deformation of the weaker vehicle could be sufficiently large to intrude into the occupied volume of the operator or passenger compartments. As a result, the strength incompatibility has the potential for increased risk of injury for passengers in the weaker vehicle. The design strategy of many modern rail vehicles is to reduce vehicle weight and incorporate crashworthiness design features to improve safety. This is in contrast to an older design approach where strength requirements, such as a high buff strength, were included to ensure structural integrity. The objective of this study is to assess the collision risk for a mixed rail fleet of different vehicle designs. Collision safety is investigated for three different vehicle types. The crash scenarios investigated include vehicle to vehicle collisions between newly designed cars, between older designed cars, and between a mix of new and old designs. To quantify risk, parameters such as cab crush strength, occupant volume strength, and collision speed are varied in computer crash simulations to uncover potential safety problems associated with mixed car operation. Results from these parametric analyses are presented and utilized to guide the development of new crashworthiness specifications for mixed fleet operation.

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