The strong interest in producing lightweight car bodies in aluminium has prompted the need to understand the behaviour of typical crash members fabricated using mainly AA5000 and AA6000 materials. In studying the sometimes complex impact load cases, it is often useful to examine the axial and bending collapse modes seperately in order to assess the geometric and material influences, and this is the approach taken in this paper. A number of organisations have reported various mechanistic approaches to predicting performance in axial and bending collapse, and our method has been to assess, and where necessary, refine the best of these for aluminium sections in order to produce effective design guidlines for the automotive industry. This work is largely complete for axial crush and examples of design application from concept to structural testing are given. This work is less advanced for bending collapse, but this paper illustrates the principal modes encountered and the design implications for section geometry and material selection.