The utility model belongs to railway contact bridge steel column hangs upright construction operation field, concretely relates to apply to simple and easy electric motor car of bi -directional motion formula railway transportation of single line bridge, including plate holder, running gear and power device, running gear includes the roller bearing and connects in the walking wheel at roller bearing both ends, power device includes generator, motor and belt drive unit, it has two sets of control switch to connect in parallel on the motor, and the front and back diagonal angle department in plate holder along advancing direction is installed to two sets of control switch symmetries, belt drive unit includes action wheel, driving belt and two from driving wheel, and the action wheel is installed on the output shaft of motor, corresponds one installation from driving wheel on two roller bearings respectively, and two are passed through driving belt from the exclusive formula of driving wheel and are connected with the action wheel. The utility model discloses a two sets of parallel switch carry out front and back end control, realize that the fore -and -aft direction of vehicle traveles, use in a flexible way when the transportation steel column, need not reverse end for end just can control the handcart forward backward.