The paper describes the detailed crash investigation of rear underrun crashes, including occupant injuries; the development of theoretical analysis of the forces acting on a barrier during an impact from a car; and the design, development and crash testing of an effective barrier. One aim of the project was to demonstrate that an effective, lightweight and inexpensive barrier can be fitted to the rear of trucks. These findings were compared with existing design standards for rear underrun barriers and significantly upgraded performance requirements were recommended to be adopted as a new standard for Australia.