Expanding on what has been said - but still a very simple explanation.

Each section of a main track has some sort of authority that you must have to occupy it. The basic premise of the authority is that it must somehow allow movement without a head on or rear end collision, or tangling with men and equipment.

Yard Limits is a main track authority. Simplified explanation - A train or engine may use the main track within Yard Limits at restricted speed.

Rule 6.27 Movement at Restricted Speed
When required to move at restricted speed, movement must be made at a speed that allows stopping within half the range of vision short of:
• Train.
• Engine.
• Railroad car.
• Men or equipment fouling the track.
• Stop signal.
or
• Derail or switch lined improperly.

When a train or engine is required to move at restricted speed, the crew must keep a lookout for broken rail and not exceed 20 MPH.

Comply with these requirements until the leading wheels reach a point where movement at restricted speed is no longer required.



Restricted Speed is somewhat comparable to trying to drive through a narrow, crowded and sometimes very busy parking lot where everyone is trying to get through without hitting anyone else. You and everyone else has to pay attention or there will be trouble.

Track Warrant Control (TWC) is another form of main track authorization. A Line 4 might state "Work between North Yard Limits South Fork and Northtown". This is the most desirable warrant for a train crew because it gives them sole occupancy and allows them to move in either direction at maximum speed. In the original example, this would allow the daily local to occupy the branch without any other authority from the dispatcher until they returned back to Yard Limits and cleared their warrant. Where movement in both directions may be required and no other movements are needed in the immediate future, a Line 4 is commonly used.

A sample Line 2 might state "Proceed from North Yard Limits South Fork to Northtown". This warrant only gives the train permission to proceed northward to Northtown, and it would have to obtain a new warrant to get back home: "Line 1 Track Warrant 1 is void Line 2 Proceed from Northtown to North Yard Limits South Fork". The advantage on a branch with a Line 2 is that the dispatcher can authorize another train or track inspector (or other MofW) behind them, as he can have the preceding train "roll up" their track warrant to use the track behind them they are clear of. On a busier territory, a dispatcher can't authorize more than one movement within the limits of a Line 4 Work Between unless they add a Line 11 (limits jointly occupied with other trains) and/or Line 12 (limits jointly occupied with men or equipment) which requires everyone to be at Restricted Speed in the joint limits.

In ABS territory, a dispatcher can issue an unlimited number of Line 2 authorities as long as the trains are all moving in the same direction as the ABS will protect against a rear end collision. In dark territory, a preceding train must "roll up" its warrant and release the track it is clear of behind it. For example, SP 5103 North has a warrant with a Line 2 from South Fork to Northtown. SP 5103 reports it is complete by Midway. The dispatcher can now issue a following train a Line 2 from South Fork to Midway, or a Line 4 between South Fork and Midway.

A defined point, station or milepost can be used as the limits of a warrant. It is still within the rules to issue a warrant Line 2 from South Fork to Midway. Assuming South Fork was in Yard Limits and Midway was a siding designated in the Timetable, the train could use the Yard Limits rule to leave South Fork. Its authority at Midway would only be to the first (South) Siding Switch, unless a Line 8 "Hold Main Track at Last Named Point" was included which would allow it to occupy the main at Midway up to but not fouling the far (North) Siding Switch. Instead of a Line 8, it might have a line 10 added telling it to "Clear Main Track at Last Named Point" meaning it would have to use the siding, junction or yard to clear the main.

During the coal boom, many of the new hires could not grasp the basic principles of where the limits of their warrant began and ended and there were problems. This was also being transferred to computerized dispatching which had trouble with the same logic (what a surprise). As a result, most railroads will not issue a warrant with the end limits simply as a station name for any siding or within yard limits. Instead of "Line 2 Proceed from South Fork to Midway Line 8 Hold Main Track at Last Named Point" (which is still legal according to the GCOR), you are more likely to see "Line 2 Proceed from North Yard Limits South Fork to North Siding Switch Midway".

Yard Limits is not included as part of a DTC block, typically there was a different DTC block on each side. Often Yard Limits were replaced by its own DTC block (Alturas for example). If things got busy, the dispatcher could issue authority Joint With in a DTC block which required everyone to be at restricted speed. Many of the smaller Yard Limit territories have been discontinued since flag protection is no longer required.

Yard Limits are common in ABS and Double Track territory, but the their rules as well as Yard Limits' requirements must still be respected. I wasn't aware that CTC was now included in Yard Limits, so it was a surprise to me since the concept of CTC rules basically conflict with Yard Limit rules and don't present a clear advantage. A quick look in the GCOR First Edition makes no mention of CTC in Yard Limits, just ABS. The Fourth Edition does specifically mention CTC in Rule 6.13 as does later editions.

I wouldn't advise treating CTC within Yard Limits just like any other CTC, because there is a definite rule difference that could be used as a trap by your friendly neighborhood weed weasel. Part of Rule 6.13 currently states: "In CTC Territory - Where yard limits are in effect in CTC territory, the control operator must authorize any movement on the main track. Reverse movements within the same block may be made as outlined in Rule 6.4.1 (Permission for Reverse Movements)." No surprise here since the CTC requirement to obtain a control operators authority applies. But before that, it states: "All movements entering or moving within yard limits must be made at restricted speed unless operating under a block signal indication that is more favorable than Approach. Upon observing or having advance knowledge that a block signal may require restricted speed due to yard limits, if entering or within yard limits, the movement must be at restricted speed at that block signal, or as soon as possible thereafter, consistent with good train handling."

This is similar to the old rule that only applied to Yard Limits and ABS, but considering the definition of "Block Signal" it now applies to CTC and ABS. So if you are in or approaching ABS or CTC with Yard Limits, and you have a hard yellow as part of the approaching signal or anything requiring you to possibly stop at the next signal - it now actually requires Restricted Speed regardless of the signal's normal meaning outside Yard Limits.

I really don't understand the advantage or reason to have Yard Limits within CTC. This odd exception may be a factor in a future accident.