Method for operating at least one axle of a road-vehicle tractor-trailer combination, wherein the axle (6; 11) is arranged outside of a tractor (2; 8) of the road-vehicle tractor-trailer combination on at least one vehicle (3; 10) pulled by the tractor (2; 8), wherein data relating to the current driving operation state of the road-vehicle tractor-trailer combination are ascertained, wherein a temporary drive demand in addition to the drive (5:9) of the tractor (2; 8) is ascertained from said data, wherein the axle (6; 11) of the pulled vehicle (3; 10) is designed as a drive module and temporary driving axle with a drive unit that can be activated in a controlled manner, wherein the drive unit is automatically activated and connected in the case of an ascertained temporary drive demand so that the axle (6; 11) is switched thereby from an idler axle operation to a temporary driving axle operation, characterized in that the drive module is activated depending on automatically determined communication options with the tractor (2, 8) in such a way that - when a lack of communication option with the tractor (2; 8) is determined, the drive module independently evaluates a separate sensor system and independently from this makes the decision to connect the drive unit, - in contrast, when communication between the tractor (2; 8) and the drive module is determined to be present, specifications from the tractor (2; 8) are used to connect the drive unit, - in both above cases, it is checked and determined whether the tractor (2; 8) is coupled to the drive module for the purpose of energy supply, if not a required energy store of the drive module is filled only by recuperation during braking and/or downhill travel and emptied by an axle drive, otherwise if there is a connection to the tractor (2; 8) for the purpose of energy supply, this is used directly and/or an energy store is additionally filled or emptied by an energy transfer between the tractor (2; 8) and the drive module, and - in any case, the drive unit is activated temporarily to support the drive during starting procedures and/or on inclines and to recuperate during braking and/or descents. wherein data relating to the current driving operation state of the road-vehicle tractor-trailer combination are ascertained, wherein a temporary drive demand in addition to the drive (5:9) of the tractor (2; 8) is ascertained from said data, wherein the axle (6; 11) of the pulled vehicle (3; 10) is designed as a drive module and temporary driving axle with a drive unit that can be activated in a controlled manner, wherein the drive unit is automatically activated and connected in the case of an ascertained temporary drive demand so that the axle (6; 11) is switched thereby from an idler axle operation to a temporary driving axle operation, characterized in that the drive module is activated depending on automatically determined communication options with the tractor (2, 8) in such a way that - when a lack of communication option with the tractor (2; 8) is determined, the drive module independently evaluates a separate sensor system and independently from this makes the decision to connect the drive unit, - in contrast, when communication between the tractor (2; 8) and the drive module is determined to be present, specifications from the tractor (2; 8) are used to connect the drive unit, - in both above cases, it is checked and determined whether the tractor (2; 8) is coupled to the drive module for the purpose of energy supply, if not a required energy store of the drive module is filled only by recuperation during braking and/or downhill travel and emptied by an axle drive, otherwise if there is a connection to the tractor (2; 8) for the purpose of energy supply, this is used directly and/or an energy store is additionally filled or emptied by an energy transfer between the tractor (2; 8) and the drive module, and - in any case, the drive unit is activated temporarily to support the drive during starting procedures and/or on inclines and to recuperate during braking and/or descents. - when a lack of communication option with the tractor (2; 8) is determined, the drive module independently evaluates a separate sensor system and independently from this makes the decision to connect the drive unit, - in contrast, when communication between the tractor (2; 8) and the drive module is determined to be present, specifications from the tractor (2; 8) are used to connect the drive unit, - in both above cases, it is checked and determined whether the tractor (2; 8) is coupled to the drive module for the purpose of energy supply, if not a required energy store of the drive module is filled only by recuperation during braking and/or downhill travel and emptied by an axle drive, otherwise if there is a connection to the tractor (2; 8) for the purpose of energy supply, this is used directly and/or an energy store is additionally filled or emptied by an energy transfer between the tractor (2; 8) and the drive module, and - in any case, the drive unit is activated temporarily to support the drive during starting procedures and/or on inclines and to recuperate during braking and/or descents.