A device for sensing and measuring a transient load, such as a load imposed by at least one wheel on an axle of a passing vehicle, comprising a flexible and resilient mat formed of a dielectric and elastomeric material and adapted to be engaged by the load, and at least two vertically spaced capacitor electrodes embedded in and extending over substantially the entire operative area of the mat. The electrodes are connected to a device for detecting variations in the electrode spacing owing to transient loads. Void areas are located in the body of the mat to provide for mat deformation that is linearly proportional to the magnitude of the applied load. Preferably, the void areas are uniformly distributed in the mat and extend substantially from one of the electrodes to the other electrode.