Approximatively 700 000 bicycle scooters (mopeds) are registred in Switzerland (engine displacement 50 ccm,top speed 30 km/h, no licence).They may be driven by persons older than 14 years. Over 10% of all traffic fatalities in Switzerland involve drivers of these vehicles.

133 drivers were killed in 1975 and 4491 severely injured. Detailed results of a one year study of all accidents involving these mopeds in the city of Ziirich are presented. As in accidents with heavy motorcycles the most frequent cause of death is a trauma of the skull and / or the brain. Therefore headinjuries are analysed whereby special atention is given to drivers protected by helmets. Integral helmets seem to give the best protection.

The standard procedure of testing helmets in Switzerland is discussed. The conditions under which a helmet is pushed away by a wheel rather than rolled over are examined. For this purpose some aspects of the interaction between helmet wheel and ground are investigated mathemathically and experimentally. It is shown that the main parameters are the angle between wheel direction and the tangent plane in the contact point of the helmet as well as the diameter ratio between wheel and helmet.