An investigation termed THESEUS which is scheduled to last for several years has been initiated by the German Federal Minister for Research and Technology. This investigation is intended to generate measures designed to improve tank trucks transporting hazardous substances. For this purpose, the safety of the overall system consisting of vehicle, tank components and safety devices, participants in the accident and the type of accident will be considered. Relevant accident statistics and analyses of accidents by teams involved in the project will create the parameters for the experimental and theoretical investigations. Crashes will be simulated with original tank vehicles in the form of vehicle-to-vehicle collisions and overturning tests which have proved to be important since hazardous goods are frequently released. The experimental simulation of the overall vehicle will be supplemented by the systematic testing of tank components in order to examine the behaviour of the walls when exposed to puncturing and flat loads. These investigations should result in sound, simplified test methods for the approval of tanks. The experiments will be accompanied by numerical calculations. The first step will be to validate the mathematical model with experimental results and then to calculate conditions not covered by experiments. The second step should provide a better understanding of the mechanisms of deformation and the criteria of rupture. In addition to this, the driving behaviour of tank vehicles will be investigated by means of objective driving maneuvers such as steady-state turning, step steering input and sinusoidal steering input. The most important parameter to be varied will be the loading condition of the tank vehicle. The most significant results are expected to be the non-steady-state overturning limits of the vehicles under investigation. These limits will be compared to those obtained under steady-state conditions during tests on a turntable. These experiments will also be supplemented by numerical calculations. The numerical model will be validated by experimental results obtained with a modern truck-trailer combination with a low center of gravity. The model will then be used to study the influence of parameters. The objective of the investigation which commenced in summer 1990 is described and the results which have been obtained so far are presented.