An improved sliding door assembly is provided to be installed adjacent to a doorway having a split jamb. The door leaf is supported on a door carrier that extends between a top edge and a bottom edge of a frame, while the frame has at least one track configured to guide the door carrier and a rotatable tie rod mounted to the door carrier extending 5 between the top edge and the bottom edge of the frame and having a pinion gear at each end to engage with a rack at the top edge and bottom edge respectively such that engagement of the pinion gears synchronises the motion of the door carrier.

A platform screen gate system having a tower, a gate secured to the tower. The gate is movable between an open position, to facilitate access to and from the platform, and a closed position, to block access to and from the platform. The system further includes at least one roller secured to the tower and a track secured to the gate. The track is supported by and movable on the least one roller such that the gate cantilevers from the tower and remains above the platform when the gate is moved between the open and closed positions.

A modular door frame having a base transom horizontal and a plurality of vertical frame members. The modular door frame can further include a secondary transom. The secondary transom can be a sliding door track that is superimposed over the base transom horizontal. In the implementation of the modular door frame, base transom horizontal can be a stopper transom horizontal configured for a hinged door and can include a stopper. The secondary transom is superimposed over the base transom horizontal to avoid occluding portions of the door (below) and a clerestory (above). The clerestory and door may be glass. The secondary transom is secured to the base transom horizontal by inserting a hook on the secondary transom into a channel in the base transom horizontal. The connection is a secure, cantilevered connection that does not require tools or fasteners.