Dual level access door system for railway vehicles

A door system for a railway vehicle having a door opening and a stairwell extending downwardly from a vehicle floor level to a bottom end of said door opening, said door system comprising a sliding door displaceable between open and closed positions for selectively closing said door opening, a stairwell platform displaceable between a retracted position for clearing said stairwell and an extended position for covering said stairwell, a threshold extending laterally outwardly of said sliding door substantially at said vehicle floor level, said threshold being releasably connected to said sliding door for co-linear movement as a single unit with said sliding door between said open and closed positions when said stairwell platform is in said retracted position thereof, while remaining stationary in a functional position when said stairwell platform is in said extended position thereof for allowing high level boarding, and a lock for selectively securing said threshold to said sliding door, said lock including a catch provided on a first of said sliding door and said threshold, and a latch assembly on a second of said sliding door and said threshold, said latch assembly including a housing, a slot defined in said housing, a spring-loaded latch member mounted in said housing, said latch member having a catch engaging portion extending outwardly of said housing through said slot for movement therein, and a safety member displaceable between a first position for preventing access to the interior of said housing through said slot when said latch member is urged to a locked position thereof and a second position for at least partly clearing said slot so as to allow said latch member to be displaced to an unlocked position thereof, wherein said threshold is disconnected from said sliding door in response to a displacement of said stairwell platform to said extended position thereof.