Abstract: A power transmission system is provided for use in a platform drive mechanism of a passenger conveyor which has a conveyor frame and a plurality of laterally extending passenger platforms which are movably supported for driven movement about an endless path on the frame and engaged with a pair of circuitous drive chains disposed on opposite sides of the conveyor frame The transmission system has a multiple stage reduction gear drive positioned outboard of the passenger platforms and directly coupled between the drive chains and a motor for driving the passenger platforms in response to energization of the motor. A sprocket assembly has a drive shaft which extends laterally across the conveyor frame and mounts a pair of axially spaced sprockets.