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Railroad Rules, Signalling, Operations:

Direct Traffic Control

byCarsten S. Lundsten. Last updated 26-07-1998.

Contents

Introduction
The DTC Block

Movement Authority
    DirectionalAuthority
    RestrictedAuthority
    Work and TimeAuthority
    Multiple DTC Authoritiesin the Same DTC Block

    Changing Authority
    Releasing DTCBlock Authority
A DTC Example

Introduction

Direct Traffic Control (DTC) is a verbal authorization system definedby theGeneral Code of Operation Rules (GCOR), used to authorizetrains to occupy Main Tracks. DTC can be used as a stand-alone safety systemin unsignaled territories, or can be supplemented with Automatic BlockSignaling (ABS) to increase flexibility and traffic capacity. DTC is asfar as I know used by Union Pacific and CSX, on the former Southern Pacific,Chicago and North Western and Seaboard Coast Line. Direct Traffic Controlon the former Chicago and North Western lines was quickly replaced by TrackWarrant Control after the Union Pacific takeover, as TWC is the systemsused by Union Pacific. If is not unlikely that DTC will also disappearfrom the former Southern Pacific lines within the next few years. TWC isused on the other western railroads and is a more flexible - but also morecomplex - system.

Direct Traffic Control divides the line into fixed DTC Blocks. Trainsare authorized to occupy specific DTC Blocks. DTC rules specify fixed wordingfor messages concerning the grant or release of DTC Blocks. The train crewsmust keep a written note of the DTC Blocks their train is authorized tooccupy. The train releases the DTC Block Authorities after it has clearedthe DTC Blocks.

The DTC Block

A DTC line is divided into fixed DTC Blocks. The DTC Blocks are named,typically after a Station at one end of the DTC Block. The extension ofeach DTC Block is defined in the Timetable and is also marked by linesidesigns.

A line with regularly spaced Sidings will usually be divided into DTCBlocks extending from one Siding to another. At some locations, however,the line between two Sidings has been subdivided into 2 or more DTC Blocks.Below is shown an example of a DTC line:

The Stations Anna and Danby have a Siding for meets. Bolo is just anintermediate Station while Coyote Jct is the junction of another line.

DTC Block boundaries at Anna and Danby are at one end of the siding,in this example the east end. Placing the boundary at one end of the Sidinghelps speed up certain meets, as will be shown later. The DTC Block boundaryat Bolo it at the Station sign. Many stations like Bolo have once had aSiding, and therefore the DTC Block boundary may still be where it wasin the days of the Siding. At Coyote Jct it is most practical to placethe DTC Block boundary so as to facilitate trains going on or off the branchwithout occupying the DTC Block to the West. In the example the DTC Blocksare named after the Stations at the east end of the Blocks, thus definingthe DTC Blocks "Anna", "Bolo", "Coyote", "Danby" and "Eve".

Movement Authority

A DTC Block Authority is issued in the following steps, usually using radio:A DTC Block Authority cannot not be considered valid until the dispatchersays "<Train>, that is correct.".

Directional Authority

Directional Authority authorizes a train to occupy one or more DTC Blocks,moving in a specified direction. A train having been issued a DirectionalAuthority is not allowed to move backwards in the DTC Block. But sincea DTC Block is only the Main Track, a train may set back into a spur orsiding.

To illustrate how a Directional Authority is issued, we'll use the examplebelow. A train (7241 East) has Authority in the DTC Block Anna only, andthe Dispatcher is to issue Directional Authority to DTC Blocks ahead:

To give Directional Authority in one DTC Block, the following wordingis used:

After receiving "That is correct", 7241 has Directional Authority in DTCBlock Bolo as well:

To give Directional Authority in two DTC Block, the following wordingis used:

To give Directional Authority in more than two DTC Blocks, the followingwording is used:

Restricted Authority

In dark territory a train may be issued Restricted Authority to followbehind a train granted Directional Authority to that same DTC Block. Movementmust be made at Restricted Speed. Restricted Authority may only be grantedone train in a DTC Block. Restricted Authority may only be granted afterthe Dispatcher is has assertained him/herself that the train ahead haspassed the point where the train given Restricted Authority will enterthe DTC Block. When the train ahead has released the DTC Block in question,the requirement for Restricted Speed may be canceled, converting the RestrictedAuthority to a Directional Authority.

Restricted Authority is typically used to allow a train to pull outof a Siding after being overtaken. If the train has to line a switch backbehind itself, it can pull out on the Main on the Restricted Authority.In most cases the train ahead has cleared the DTC Block before the secondtrain is ready to depart.

To give Restricted Authority in one DTC Block, the following wordingis used:

Canceling the requirement for Restricted Speed is done using the wording:After receiving "That is correct", 7241 has Directional Authority in DTCBlock Bolo as well.

Work and Time Authority

Work and Time Authority permits a train to occupy the DTC Block(s) andmove in either direction. Several trains may be present in the DTC Blockunder Work and Time Authority, in which case movements must be at RestrictedSpeed. A second train may not be issued Work and Time Authority to a DTCBlock before the train already issued a Work and Time Authority is informedthat the DTC Block will be jointly occupied. As the name suggests, a Workand Time Authority is time limited, i.e. the train must have cleared theDTC Block(s) before that time expires. The DTC Block(s) cannot, however,be considered clear until they are released by the train.

Work and Time is issued by the dispatcher using the wording:

Work and Time may be granted in several DTC Blocks, using similar wordings.

Work and Time may be issued only if:
 

  • The DTC Block is clear.
  • Or(in ABS territory only) the DTC Work and Time Authority willnot take effect before the arrival of a train running on Directional Authorityin the DTC Block. 
  • Or the DTC Block has been allocated under Work and Time Authorityto another train which is informed that the DTC Block will be jointly occupied.

Multiple DTC Authorities in the SameDTC Block

Only one DTC Authority may be issued issued in the same DTC Block, exceptin the following cases:
 
  • In ABS territory, multiple Directional Authorities may overlapinthe same direction, as the ABS will protect following trains from eachother.
  • In Dark Territory, as specified for Restricted Authority, to followanother train still in the same DTC Block. After the first train releasesthe DTC Block, the Dispatcher may upgrade the Authority to a DirectionalAuthority.
  • At meets, when Directional Authority will not take effect before arrivalof an opposing train. The DTC Authority must include the words "...afterthe arrival of <train>".
  • Under Work and Time Authority when trains are instructed to move at RestrictedSpeed.

Changing Authority

If it becomes necessary to change the DTC Block Authority previously grantedto a train, a new Authority is granted in the specified manner. After the"That is correct" message, the previous Authority to the DTC Block(s) inquestion becomes void.

Releasing DTC Block Authority

When a train has cleared a DTC Block, the DTC Block must immediately bereleased to the Dispatcher, unless the Dispatcher has specified that immediaterelease is not necessary.

A train may release a DTC Block only when the entire train has clearedthe DTC Block. If a train clears the DTC Block by entering a SecondaryTrack, the switch must be lined back to the Main Track before releasingthe DTC Block.

To release one DTC Block, the following wording is used:

Similar wordings are used for the release of more than one DTC Block, followingthe pattern for issuing Authorities.

A DTC Example

The following is an example of how Direct Traffic Control may be used tocontrol an unsignaled, single track, line. The example line is similarto what has been shown above, with the two sidings Anna and Danby, thoughDanby is now controlled by CTC. In between are the stations Bolo and CoyoteJct. The timetable text would read something like:

DTC in effect between <Somewhere West> and Danby.

CTC in effect between west switch Danby and <Somewhere East>.

This means that the siding at Danby is under CTC, while the siding atAnna has manual switches.

Two trains are to meet at Anna. The trains will be called585 East(Eastbound) and5032 West (Westbound). 585 East will be arrivingfirst to the meet and is to take Siding. Since the switches are hand-thrown,the 585 East has to line the switch back after pulling into the siding.This means leaving the Conductor behind to line the switch back, afterwhich he/she will have to walk up to the locomotive.

The DTC Authority for 585 East, from a DTC Block somewhere west couldread:

585 East would also be instructed to take siding at Anna and, since there'slittle other traffic, that it need not release its DTC Blocks before clearingthe Anna Block.

5032 West is somewhere beyond Danby and has not yet been issued a DTCAuthority to go further than Danby. Only the signal into the main trackat Danby has been cleared but even if the signals were clear through Danby,5032 West would not be permitted to depart Danby without a DTC Authority:

As 5032 West approaches Danby it is time to issue a DTC Authority. Since5032 West is an ordinary train and no other trains are ahead, 5032 Westis issued a Directional Authority to the meet at Anna:

5032 West is also instructed that it need not release its DTC Blocks beforeclearing the Bolo Block. When the DTC Authority has been issued, the dispatcherclears the signals out of Danby:

585 East has how arrived at the west switch at Anna and prepares tohead into the siding. 5032 West is approaching Danby:

585 East is now in the siding and releases its DTC Blocks:

With 585 East in the clear, 5032 West can be permitted to continue pastAnna. The dispatcher issues a further DTC Authority to 5032 West:

5032 West now has DTC Authority in all DTC Blocks between Danby and Somewehreelsewest.Since other traffic doesn't require the DTC Blocks behind 5032 West, thereis no reason to release them one by one.

The dispatcher also issues a new DTC Authority for 585 East:

"...after arrival of 5032 West" suspends the DTC Authority until 5032 Westhas cleared the east switch at Anna:

As soon as 5032 West clears the east switch at Anna, 585 East's DirectionalAuthority comes in effect. 5032 West releases the traversed DTC Blocks:

585 East's Directional Authority comes in effect even before 5032 Westhas released the DTC Blocks to the Dispatcher.

After 585 East has pulled out of the Siding, our poor conductor willonce more have to line the switch back and walk up to the locomotive before585 East can get on the move again. The dispatcher has set up a new meetfor 585 East at Danby, but this time all controlled by CTC:


Comments, corrections and more information about DTC are very welcome. Please usethis contact form

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Text, Images and HTML: Carsten S. Lundsten.

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