shaped rails 9 secured to the lower corner regions of the central girder 1 the two couplings which connect each side girder 2 to the central girder 1 and which are each formed of rollers 8 and a rail 9 are situated symmetrically to one another with respect to the central vertical longitudinal plane a of the central girder 1 each rail 9 also has at its inwardly oriented side that is at the side facing away from the respective adjoining side girder a u shaped opening to receive rollers of a non illustrated bridge launching device providing for an initial forward displacement of the central girder 1 for this purpose the central girder 1 which as a rule is used as the initial bridge carrier has a downwardly oriented u shaped opening 10 it is feasible to arrange the rollers 8 in a reverse orientation that is to mount them for rotation on the rails 9 to engage preferably u shaped rails secured to the side of the respective inner lower truss 3 of the side girder 2 the side girders 2 may be advanced to span the obstacle to be bridged over the central girder 1 which has already been positioned as an initial bridge carrier preferably the individual modules of the side girders are advanced in pairs synchronously and are coupled with one another the individual modules of the side girders 2 may be of identical construction and may be therefore interchangeable in the fully deployed.