The lack of a suitable means of measuring levels of protection for car occupants in side impacts has hampered development of satisfactory designs of car to withstand impacts of this type by cars or other objects. The TRRL side impact dummy described in the paper has been designed specifically for this task and its use has been demonstrated in achieving a high level of protection for occupants of the Leyland Marina cars developed in the international car safety programme. The dummy makes possible the matching of each part of the energy absorbing inner face of the donor structure to the different loadings on the human frame, which can be safely tolerated at the shoulder, chest and pelvic regions. This paper describes the dummy and some of the testing to ascertain its suitability for impact test procedures, as well as describing how it was used to estimate levels of human tolerance to impact loadings in accidents and how it contributed to the design of the side structure of the modified Marina.A FORCE MEASURING DUMMY has been developed at the Transport and Road Research Laboratory to assess the injury potential of vehicle structures when struck almost perpendicularly in the side. It has force transducers fitted to measure lateral loadings at locations corresponding to the shoulder joint, four stations on the rib cage, the iliac crest and the hip joint. Accelerometers may be fitted in the headform, upper thorax and pelvis. This paper describes the work which has been done to date on the design and construction of this dummy, its preliminary calibration using real life accident data and its use to develop safer designs of cars.