Pneumatic propulsion system for freight and/or passenger vehicles A pneumatic propulsion system for passenger vehicles is constituted by a structural beam, composed of modular elements end-supported on pillars. The beam supports the trackway and provides an air duct for pneumatic propulsion of vehicles. A longitudinal slit in the top surface of the beam is sealed by flexible flaps and that press against each other to seal off the duct, while allowing for the passage of support mast. Airflow for propulsion of the vehicle is generated by a stationary airflow generator, which feeds the air propulsion duct by way of connecting ducts and which is outfitted with a set of four butterfly control valves that are controlled by a command and control system of flow and pressure condition in the duct which actuates the valves pneumatically, allowing automatic or manual selection of "suction" or "pressure" conditions in the duct. Shutoff valves are fitted to openings in the bottom surface of the beam to allow isolation of segments of the propulsion air duct or, alternatively, its venting to connecting ducts or to the atmosphere, allowing by means of a combination of several valves to delimit a specific propulsion air circuit. Traction of the vehicles results from the difference in pressure that is established on opposite sides of propulsion plate by the effect of the airflow generated by the generator unit. A support mast connects to a propulsion plate jointly with a traction arm which transfers the resultant tractive force to the vehicle. Adjustable decompression panels assembled on the propulsion plate assure that a maximum safe pressure differential limit is not exceeded, said limit being controlled by the action of a set of springs positioned on both sides of the propulsion plate. Powered motorcycle lift/stand A hydraulically, pneumatically, electrically, or engine operated motorcycle center stand assembly having a ground-contacting lower stand unit rotatable about an axis on an upper stand unit. Parking is accomplished by rotation of said lower stand into said ground-contacting position, followed by downward pivoting of said upper stand unit, thereby raising said rear end of said motorcycle. The stand is raised by reversing the sequence. Ground contacting area, stand width, and stability are increased while simultaneously retaining maximum road clearance. Hovercraft motorcycle In a preferred embodiment, a hovercraft motorcycle for travel over a ground surface, comprising: a body portion having a front end, a rear end, a longitudinal centerline extending from the rear end to the front end, and a lower surface spaced above the ground surface; a generally horizontal, continuous, inflatable, resilient tubular member attached to, disposed around, and depending from the lower surface of the body portion having an air inlet port; the generally horizontal, continuous, inflatable, resilient tubular member having an air inlet port; an air plenum chamber defined between the tubular member, the lower surface of the body portion, and the ground surface; an apparatus to supply pressurized air to the air plenum chamber; a front wheel assembly, attached to the front end of the body portion and on the longitudinal centerline of the body portion, having a front wheel mounted thereon; and a rear wheel assembly, attached to the rear end of the body portion and on the longitudinal centerline of the body portion, having a rear wheel mounted thereon. Lateral stabilizer for two-wheeled vehicles A system for laterally stabilizing a two-wheeled vehicle includes a pair of outrigger struts having respective outrigger wheels on opposite sides of the rear wheel, vertically movable between raised and lowered positions relative to a supporting structure, the struts each being connected by a transverse strut shaft for unison vertical movement and extending forwardly of the strut shaft; an electric motor driven actuator mechanism including a rotatably mounted lead screw shaft that is pivotably mounted relative to the supporting structure, a drive nut threadingly engaging the lead screw shaft that is connected to the strut shaft for driving the wheels between the raised and lowered positions in response to rotation of the lead screw shaft. A controller for electrically powering the motor includes pilot circuit paths of a bidirectional motor bridge circuit, the pilot circuit paths being electrically powered only when motive power of the vehicle is enabled, the actuator mechanism in combination with the motor having sufficient drag and mechanical advantage whereby the outrigger wheels are locked from movement between the raised and lowered positions in the absence of electrical power to the motor. Limit switches are connected for inhibiting corresponding ones of the pilot circuit paths for preventing overtravel of the outrigger wheels.