A bumper having a hollow section and attached to it mounting brackets for attaching the bumper to a vehicle\u2014in particular on longitudinal beams of a private car\u2014is such that section walls that are spaced apart form a compression strut and a tensile strut and a pair of flanking walls joining the said struts make up the hollow section. The reliability of the stored information is checked periodically using data verification operations whose results are saved. The system also provides for audio warnings at an intersection to protect pedestrians who may not be in a position to see visual warnings or for various reasons cannot hear the approach of emergency vehicles. Upper and lower leaf springs respectively support the holder so as to be displaceable along the optical axis direction of the lens unit; a base for supporting the yoke and the lower spring.