RAILROAD SIGNALS of the U.S.


TRAIN CONTROL METHODS
by (mostly) SIGNALS
 

Manual

Train Orders

  
Train Order signals from a 1969 B&O/C&O Rulebook

  
Train Order Semaphore at the North Carolina Transportation Museum/Spencer NC.

  
Train Order Semaphore at the Radial Railway Museum in Milton ONT.

Track Warrant Control (TWC)

A Tack Warrant is a verbal form of authorization, used to authorize trains to occupy the main tracks.  Orders are  usually given by radio.  TWC is a verbal authorization system defined by the General Code of Operating Rules (GCOR).

Track Warrants can be used as a standalone dispatching and safety system in unsignaled territories, or can be supplemented with ABS to increase flexibility and traffic capacity.

The dispatcher reads the track warrant info (and instructions) to a crew member of a train, who then writes the information down on a form standardized by the railroad.  The same crew member then reads back the info back to the dispatcher for verification.  If what the crew member read back was OK, the dispatcher says "OK", and gives the time and his initials.  The crew member then writes down the "OK" time and initials on the form, and repeats them back to the dispatcher.  The track warrant is not in effect until the "OK" time is shown on the form.

For an in depth discussion of TWC, check out: http://www.lundsten.dk/us_signaling/twc/index.html

Thanks to Mark Engels, Bob Poortinga, and Carsten S. Lundsten.

Direct Traffic Control (DTC)

Direct Traffic Control is similar in principal to TWC (and also defined by GCOR), except the line is divided into fixed DTC blocks, and authorization is given to occupy specific DTC blocks. These blocks are typically named after a station in that block.  A line with regularly spaced sidings will typically be divided into a DTC Block extending from one siding to the next - on occasion, there may be more than one block in between sidings.  DTC rules specify fixed wording for messages concerning the granting or release of DTC blocks.  Train crews must keep a written note of the DTC blocks their train is authorized to occupy.  The train releases the DTC Block Authorities after it has cleared the DTC Blocks.

Roads using DTC include:
     the Union Pacific
     CSX
     the former Chicago and North Western
     the former Southern Pacific
     the former Seaboard Coast Line

For an in depth discussion of DTC, check out: http://www.lundsten.dk/us_signaling/dtc/index.html

Thanks to Mark Engels, Bob Poortinga, and Carsten S. Lundsten.

Here is an interesting recollection of DTC I received by email:

 As I grew up in the early 80's, I learned that trains running past my father's hardware store in the Detroit area were dispatched under T&TO operation. (Grand Trunk Western, Mt. Clemens Sub at Richmond between Port Huron and Detroit.) Sometime in the mid-80s, DTC was put into effect.  I was just starting to listen to the scanner at the time and recall four DTC blocks being used. A pair of signs delineating two blocks was right near my father's hardware store.  Became very helpful when determining whether the local might put in an appearance on any given afternoon to switch the elevator in town.  If a train got the RICH block in the mid-to-late afternoon, there was a pretty good chance it was the local.

I'd gone away to college in the late 80's...by the time I moved back into town to work after graduation, the DTC signs were gone. I had a chance to get reacquainted with the operations in the early 90's as I rented one of my dad's apartments above the hardware store.  TWC is used on this same subdivision now with a small "island" of CTC on either side of the Haven controlled siding.  As I recall, the distant signal can be viewed from the street crossing near where my father's hardware store was located. Not sure when exactly the change had  taken place, though Brother Burgett might remember when (given that's part of his territory now.)

Automatic Block Signaling (ABS)

Centralized Traffic Control (CTC)

Centralized Traffic Control is a system of control whereby the railroads employ a dispatcher at a central point, and the dispatcher remotely controls the signals and the routing of trains, and the engineer of a train must obey the signals.  CTC bypassed the need for local operators and eliminated written (train) orders.

CTC systems built upon the proven technology of the track circuit, and added coded transmissions over a pair of wires to control multiple relays in the control area, eliminating the need for a separate pair of wires to control every one or two functions (see Note 1).

The first CTC installation was in 1927 by GRS (picture below) on a 40 mile section of New York Central track between Stanley and Berwick OH, with the CTC control machine located in Fostoria OH (great railfanning place with their triple diamonds, BTW!).


Picture from pamphlet #1364 - "A Centennial - History of ALSTOM Signaling Inc." 1904-2004

When the system was first implemented, the control points were towers located along the railroad right-of-way.  Today, the control points are massive installations at (usually) one location for the entire railroad, such as Jacksonville FL for CSX, Omaha NE for the UP, and Fort Worth TX for the BNSF, and are called operations centers.  Operations centers are the "thing" nowadays, as even the tiny Baltimore and Minneapolis Light Rail Systems have them, each with three screens.

Note 1: By using polar relays, designers could control two functions over a pair of wires instead of just one.  A simple circuit using a standard relay, whether AC or DC, could only control one set of contacts (polarity made no difference).  With a polar relay, you could control two sets of contacts, depending on the polarity of the control voltage.  You can do the same thing at home by using a step down transformer as a voltage source, and then using a diode to rectify the AC into pulsating DC.  Depending on the orientation of the diode, you could have a "plus" polarity, or a "negative" polarity.  At the other end of the circuit, you could use similar diodes, which would "steer" the control voltage to the appropriate device you wanted to control or activate.  On the railroads, using DC for the example, the controlling relays would reverse both wires of the pair going out to the next block, producing either a "plus" or negative" voltage on the same wire, which would then pull the armature of the relay one way or the other.  This is also the principle behind the searchlight signal mechanism.  In a simple three aspect, single head signal such as used on the Western Maryland, and the Pennsy (on lightly used single track lines), basically, all that was needed was a single pair of wires between the blocks for each direction.  If the pair was not energized, it "sent" a "stop" to the next block, as no voltage was a failsafe condition, and the receiving end interprets that as "red".  Applying voltage to the pair one way would send an "approach" signal to the preceding block, and reversing the voltage would send a "clear".

Route Signaling - an overview by those guys at the Railway Technical Web Pages

A Few CTC Installations

To give you some idea the size of the operations center at CSX's Kenneth C. Duford Transportation Center, it dispatches and monitors some 1400 trains a day over it's 20,000 mile system.  To accomplish this, CSX employs approximately 500 employees, which is roughly one-sixth of the staff in Jacksonville.  The traditional CTC board has been replaced by computer consoles for each of the operators, and some 150 rear projection screens adorn the outside perimeter of the 150 foot diameter control room.  According to the article, the 32 dispatchers are on the first and third floors of the center.  Power managers, chief dispatchers, and locomotive mechanical personnel are on the second floor.  On the top floor are the center's general manager, assistant general manager, and Amtrak passenger train coordinator.

It took CSX two years to build the center, and cost approximately 23 million dollars.  When it was first completed, the only segment of the system not controlled from this room was the Clinchfield Route.

This info came from an article I found on the web at http://findarticles.com/p/articles/mi_m1215/is_n5_v190/ai_7627983
referencing an article from Railway Age in May 1989.

The Union Pacific's operations center is in control of some 33,586 miles of track (as of 2003), 7,100 engines, and 153,000 freight cars.

If you have more info on UP's center please email me at toddgp30@comcast.net

Burlington Northern's James J. Hill Center north of Fort Worth was dedicated in April of 1995, controlled (then) 22,000 route miles, and cost $120M to build.  This BN facility consolidated operations at Alliance NE, Springfield MO, Minneapolis MN, and Seattle WA.  It controls 500-600 trains a day.  It contains nine 18x24 screens in a 45,000 square foot fan shaped room.

Equipment was supplied by US&S.  The Santa Fe used equipment supplied by DigiCon, and I haven't found any info yet as to what happened after the BNSF merger.

http://findarticles.com/p/articles/mi_m1215/is_n6_v196/ai_17040440

UP and BNSF opened a joint operations center in Spring TX in 1998, controlling more than 340 miles of track in primarily the Houston TX area.

I'm also looking for info on CP's (and anyone else's) operation centers!

Differences between US and British signal methods (Railway Technical Web Pages)

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New 10-6-2006
Last Modified: 27-Jan-2010