Measurement methods on the interaction of rail vehicles with track and environment have followed closely the evolution of the measurement techniques for road vehicles. Where possible similar sensors have been adopted for both road and rail modes. The gravitational forces exerted by the rail vehicle can be measured by the bending of the rail between the sleepers or by the bending of the sleepers beneath the rail (Fig. 1). It is also possible to measure the lateral and longitudinal forces exerted by the flanged wheel constrained to run along the rail.