In conventional vehicle cranes it is usually necessary in consideration of current safety regulations to provide at least two separate steering circuits for all steered axles so that, in the event of a failure of one circuit, the vehicle crane can continue to be steered by way of the other. In order to avoid that in accordance with the invention at least one steered rear axle of a vehicle crane (1) is provided with a caster (a) so that at least one axle (11-16), in the event of a steering failure, remains steerable passively by utilising the caster friction. That principle is applied in a similar manner to a module axle (2) which can be mounted to the vehicle crane (1) and which can be required for transporting additional equipment or an additional counterweight which is possibly required.