
WAYSIDE INTERFACE APPLICATION
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5-3
SIG-00-07-11 SEPTEMBER 2012 (REVISED OCTOBER 2019)
Version No.: B.2
5.2.2 Interoperable Train Control Messaging (ITCM)
The Wayside Interface Unit System relies on the ITCM to transmit the Wayside Status
Messages (WSMs) at a fixed interval. The WSMs are transmitted via the ITCM using a variety of
means. The basic requirement of the ITCM is to relay the wayside status information generated
by the WIU to the locomotive and/or back office.
Although the ITCM is not considered vital or safety critical, an ITCM failure can result in
significant and negative operational impacts to railroad service since the on-board PTC system
would be required to initiate a safe action in the event that a required signal/device status is not
known.
5.2.3 Train Management Computer (TMC)
The on-board Train Management Computer system listens for status messages along the track.
Status for every local wayside device in the on-board track database must be ‘heard’ by the
locomotive. The system continues to listen for status messages as the locomotive approaches
the monitored wayside devices.
Stale messages are detected by a synchronized timestamp. The TMC verifies message validity
and then displays the messages for action by the train crew.