System for detection and warning of a situation of a vehicle travelling in the wrong direction on a roadway segment, comprising: - geolocation means of GPS type able, in a periodic manner, to provide on the basis of a GPS signal, to calculation means the position and the heading of the vehicle in an information frame, - a cartographic database of the roadway segments of a road network, and of the directions of travel permitted on these segments, - said calculation means able, on the basis of the cartographic database and of the abovementioned position and of the abovementioned heading of the vehicle to establish respectively the roadway segment and the direction of travel of the vehicle on the latter, and to generate an alarm state, when said direction of travel is not the direction of travel permitted on this segment, - warning means (7, 9), embedded on board the vehicle, able to emit for the attention of the driver of the vehicle a warning message, after an alarm state has been established, characterized in that it comprises verifier means able, when an alarm state is established, to undertake a verification of its reliability, before the alarm state generated is communicated to the warning means (7, 9), the verifier means, with the aim of verifying the alarm state, comprise means able: - to estimate the reliability of the GPS signal as a function of predefined criteria, - when the GPS signal is estimated as non-reliable, to determine the mean heading of the vehicle established over at least two successive values of heading originating from the information frame, to compare this mean heading with the heading of the segment as stored in the cartographic database, and to determine the discrepancy between these two values. - geolocation means of GPS type able, in a periodic manner, to provide on the basis of a GPS signal, to calculation means the position and the heading of the vehicle in an information frame, - a cartographic database of the roadway segments of a road network, and of the directions of travel permitted on these segments, - said calculation means able, on the basis of the cartographic database and of the abovementioned position and of the abovementioned heading of the vehicle to establish respectively the roadway segment and the direction of travel of the vehicle on the latter, and to generate an alarm state, when said direction of travel is not the direction of travel permitted on this segment, - warning means (7, 9), embedded on board the vehicle, able to emit for the attention of the driver of the vehicle a warning message, after an alarm state has been established, characterized in that it comprises verifier means able, when an alarm state is established, to undertake a verification of its reliability, before the alarm state generated is communicated to the warning means (7, 9), the verifier means, with the aim of verifying the alarm state, comprise means able: - to estimate the reliability of the GPS signal as a function of predefined criteria, - when the GPS signal is estimated as non-reliable, to determine the mean heading of the vehicle established over at least two successive values of heading originating from the information frame, to compare this mean heading with the heading of the segment as stored in the cartographic database, and to determine the discrepancy between these two values.