The increasing number of injured or even killed pedestrians in urban traffic accidents demands the attention of automobile designers to improve the outside safety operation of the vehicles. To incorporate an effective pedestrian-protection system-such as bumper, engine hood, etc.-in the vehicle, one needs the relevant information about the injury limits of the pedestrians.It is also well known that most pedestrians, particularly at lower speeds, are injured in the region of the lower legs; therefore, it is necessary to know the injury limits between vehicle and pedestrian, and hence this investigation has been initiated.This paper reports on the mechanism of injuries of the tibia under dynamic load conditions. Some 209 tests with cadavers of recently deceased people representing the normal pedestrian population were carried out on a twin-pendulum catapult. Impact load had been brought up by bumper-shaped impact bodies; the point of impact was varied between the patella and the distal end of the tibia. During the tests, the time histories of the leg decelerations were recorded, and a pathological dissection just after the tests gave us the details of the incurred injuries. These data are further evaluated using a digital computer. The relation between the mechanical and biological properties of the test specimens were thus determined, and the influence of constitution, age, and sex as well as loading form, center of impact, and energy during the impact was analyzed.The breaking forces are shown as a function of impact velocity as well as the particulars of the injuries, depending upon physiological parameters thus describing critical limits, from which the risk of being severely injured will sharply rise. The relations between mechanical and physiological parameters allow estimation of the severity of real-world injuries through the dummy tests.