An inter-axle differential separates the drive shafts on the trailer from the drive shaft on the tractor in an articulated truck. Driveline stresses are reduced when the drive shafts are allowed to turn at different speeds. The inter-axle differential can maintain an equal or different torque split between the two axles, depending on design. In a truck with two axles, equal torque is sent to the tractor and to the trailer. In a truck with three axles, less torque is sent to the tractor and more torque is sent to the trailer. The inter-axle differential can be locked when the ground conditions are poor and full torque is needed in the driveline.