This journal article discusses about the concept of using location for the purpose of data access control. The concept can then be adapted easily by someone skilled in the art of security system to be used in a railway network setting.

Railway signaling and traffic control operated using a radio channel between trains and the central office... provides location information to the central office via radio when the train enters and leaves each zone... route requests and the zone occupancy messages representing the signal aspects (the maximum speed at which the train can proceed), not only for the zone currently occupied, but also for the zone next ahead.

Abstract: A method of automatically forming a wireless local area network (WLAN) within a group of rail cars in a train, where each rail car in the group has an access point/router. ...discovering nodes associated with each rail car for inclusion in the WLAN by discovering authorized access point/routers; grouping the discovered nodes into an inter-car bridge group; connecting all nodes in the inter-car bridge group to form the WLAN; and connecting the WLAN to a wide area network (WAN) to share connectivity to the WAN...