Abstract : This action stake is not technology for itself. It is a great help the development of new safety functions, e.g. the estimation of driver's behaviour based upon the vehicle's trajectory. This trajectory is determined via two sensors we developed. This system must not disturb the driver and should therefore remain invisible to him. The first one is a fiber Bragg grating sensor. It detects local strain due to the vehicle weight. The second one is based upon two conductors. One of them has a grater electrical resistance. The vehicle's weight creates a link between the two conductors. The resulting electrical resistance provides a lateral position estimation of the vehicle. Both of them were tested on a secondary road.