RAILforum: Passive Train Control Systems

This is topic Passive Train Control Systems in forum Amtrak at RAILforum.

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Posted by Amtrak207 (Member # 1307) on :

Passive Train Control systems have been advocated by safety agencies for quite some time now. The definition I've seen is a system which intervenes when an operating train passes a restrictive signal without reaction from the operating crew. Also known as Automatic Train Stop (ATS), I keep seeing it mentioned from place to place, so here's the post:
How does it, um, how does it work?
(I know not, my liege)
I've seen ATS shoes and possibly a reader by the side of the tracks, but how does it work? Could somebody consult the Book of Armaments for me please?

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F40PH #757099-8
March 29, 1976-August 17, 2001
Requisecat in pacis

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Around 2.5 million miles to go

Posted by rresor (Member # 128) on :

Actually, you're jumbling several things together here.

First, Automatic Train Stop (ATS) usually uses wayside magnets that energize when a signal is red. If a train passes, the magnet pulls open a valve that dumps the train air. This technology dates to the 1920s.

Second is Positive (not passive) Train Control. This is a system that consists of a GPS receiver on the loco, an on-board computer, and digital radio links to a central office. Central office grants movement authorities digitally; as train approaches authority limits, engineer is warned and then brakes are applied to stop the train short of the authority limit. This system may or may not be "overlaid" on existing signal systems. Tests are underway in Illinois and Michigan (Amtrak), South Carolina (CSX), and on BNSF.

Finally, the "scanner" you mention is part of a system of Automatic Equipment Identification (AEI). Freight cars have passive tags that are interrogated by microwave as trains pass the reader. The information (which consists only of car numbers) is passed to the railroad's train consisting software to be checked against the recorded consist.