A heavy vehicle that crosses the central reserve of a motorway may cause a severe accident. After the occurrence of such accidents in the Netherlands, a discussion started about the containment level of safety barriers along motorways. This resulted in a project aimed at the development of safety barriers that meet the highest containment level, the H4-level in the European standard EN 1317-2. After an investigation of existing H4-safety barriers, new designs were made for a rigid steel barrier, a rigid concrete barrier and a flexible steel safety barrier. The rigid barriers are widened versions of existing Dutch barriers: barriers with the so-called 'STEP'-profile. The flexible steel H4-barrier is a fully new design. In cross-section the barrier has the shape of a triangle which stands on one of its angles. If a vehicle runs into it, the barrier will turn over to a certain extent and by doing so it absorbs part of the kinetic energy. The deceleration of a colliding car is expected to be much lower (=safer) compared to that in a collision with a rigid construction. The design of the H4-barriers was made in conjunction with impact tests and heavy vehicle simulations using the VEDYAC computer model. The simulations show that the present designs meet the H4-requirements.