ATCS Address Decoding
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ATCS address begin with a single digit Address Type Identifier:

Type Description
0 Network Software and Services
1 Locomotives
2 Ground Host Processes (Dispatch, Maintenance)
3 Wayside Devices - Wireline-connected
4 Mobile Addresses (Work Crews, Hi-Rails)
5 Wayside Devices - RF-connected
6 Trucks and Personal Portable Terminals
7 Wayside Devices - RF-connected
8-9 Reserved for Expansion

The next three digits of the address represent the AAR-assigned railroad number: (a more complete listing may be found here).

Number Railroad
022 Atchison Topeka Santa Fe
340 ATCS Shared Network
400 Kansas City Southern Railway Company
721 Southern Pacific Transportation Company
802 Union Pacific Railroad Company

The meaning of the remaining digits varies by Address Type:

Address Type Format Description
0,2 NN Network Node Number
  DDDD Addressed Device Identifier
1,4 XXXX Locomotive or Work Crew Number
  DD Addressed Device Identifier
3,5,7 XXXXXX WIU / Control Point ID
  DD Device Number
  XX Object Number
6 XXXXXXXX Truck or Terminal Number
  DD Addressed Device Identifier