Abstract: A step-platform operator 17 for transit vehicles for driving a step 19 and a platform 18 between open and closed positions, includes a reversible drive motor 42 driving the step and platform through a lever and linkage for providing differential motion between step and platform during the last portion of the closing cycle and the initial portion of the opening cycle and allowing a mechanical interlock between step and platform in fully closed position. Both platform and step are driven from a single drive unit. Additionally, the lever and linkage assembly utilizes the weights of the platform and the step to counterbalance each other and allow the use of a low power reversible drive motor to power the system.