A wheelchair lift mechanism adapted for use particularly in the accessway of a train car is disclosed which comprises a generally planar collapsible platform assembly for receiving a wheelchair and its occupant thereon; a lift mechanism for lifting and lowering the platform between first and second elevations; a vertical support column mounted inside the train car adjacent the accessway having a support portion rotatably mounted thereto; and an extensible lift mechanism support assembly attached between the support portion and the lift mechanism frame to move the lift mechanism and platform assembly horizontally between a retracted position and an extended position away from the vertical support column to provide lateral clearance for the platform assembly outside the vehicle in the deployed position. The extensible assembly comprises a pair of parallel fixed sleeve members and a pair of parallel slide members telescopically attached between the frame and the support portion. A hydraulic cylinder controllably extends and retracts the slide members within the sleeve members.