A transportation vehicle for transporting an individual over ground having a surface that may be irregular. The vehicle has a support platform for supporting the subject and the support platform is coupled to a ground-contacting module at a pivot. While the ground-contacting module may be statically stable, balance of the support platform with respect to the ground-contacting module is maintained by motion of the ground-contacting module in response to leaning of the support platform. A motorized drive coupled to the ground-contacting module causes locomotion of the vehicle and the subject therewith over the surface, while a control loop, in which the motorized drive is included, dynamically enhances stability in the fore-aft plane by operation of the motorized drive in connection with the ground-contacting module. In the event of failure of the control loop, the pivot connection of the support platform to the ground-contacting module may be locked, thereby ensuring stability of the static assembly.