The invention relates to an anti-extraction safety device comprising, for each roller (13, 14), a rotatably fixed, preferably enveloping, shroud element (32, 33) forming a one-piece functional mechanical assembly with its counterpart. The base of the shroud elements has an extension (46, 47) which extends beneath the projecting flanks (21, 22) of the head of the guiding rail (19) in order to prevent any extraction of the guide assembly. At the front, the base of the shroud elements is preferably shaped as a lip for collecting and disposing of objects which may be present on the guiding track. The invention can be used for the rail guidance of road vehicles used for public transport.