In 2001, TNO research institute commissioned by the Dutch Transport Safety Board, investigated 12 traffic accidents with city trams that occurred in the four big cities of The Netherlands. The goal was to give recommendations for improving the traffic safety related to city trams, a subject which has hardly been studied until now. The accidents were investigated by means of an in-depth methodology that was specifically designed for this research. An on-scene investigation of the accident was an important part of the whole research. The vehicles involved were thoroughly examined and the victims, the tram driver and important witnesses were interviewed. If necessary, technical factors of the tram that possibly played an important role in the accident were investigated into more detail. All the objective information was combined to obtain a reconstruction of the whole accident. The reconstruction consisted of an accident speed and vehicle path reconstruction as well as an accident avoidance study. The data on all 12 accidents were analysed, investigating the similarities or striking differences between them. One important conclusion is that city trams are highly incompatible with most other vehicles. This concerns all three potential incompatibility factors: mass, stiffness and geometry. Taking further into account the limited tram braking characteristics and low reaction time of the tram system (approximately 1 second), city trams are potentially very dangerous in city traffic. This two-sided incompatibility will be elaborated in the paper. Furthermore, an overview of the injuries sustained by the victims will be given, combined with the most probable injury cause. Recommendations will be given to improve the active and passive safety of city trams. For the covering abstract see ITRD E137145.