The guardrail, which may take the form of various types of guardrails, is noteworthy in that it includes an impact detector/indicator, for indicating the location of the guardrail involved in an impact or accident and also for notifying the accident and the place where it occurred to a traffic control station or to public assistance personnel. The detector/indicator includes a convex protective plate (2) attached to the front of the guardrail (1) with which it is used, said plate (2) protecting a connection box (3) and a tube (4) so as together to create a means for detecting and communicating the impact that occurred, also having an indicator light (5) for flagging up the impact, said indicator (5) being positioned on a support plate (6) secured above the protective plate (2).