Western Railroad Discussion > Switch Timers

When, where and why do switches have timers? Can a dispatcher override?

This is called time locking.

If a signal has been cleared through an interlocking to allow a train to pass, all the switches on the selected route are locked in position to prevent the dispatcher from changing anything as a train approaches. This is called route locking. (Note that an end-of-siding switch is considered part of an interlocking in signaling terms, but not necessarily in the rule book.)

You can imagine the mess if a train thought it would have a straight-through route and was operating at high speed, only to have the dispatcher throw a switch just in front of a train, routing it into a siding or spur.

Where time locking comes in, is if the dispatcher wants change something, he will first call the train to ensure it can be stopped in time, then will set the proceed signal to stop. If it wasn't for time locking, all of the switches that had been locked under route locking would now be free to move. What time locking does is hold all the switches as they are until a certain period of time has passed, when they will be released to allow the dispatcher to move them. This is called "running time". The length of time is determined by how long it takes for a train to run between the approach and home signal.

Note that time locking typically applies whether there is a train approaching the interlocking or not. In some cases, where traffic is heavy, and the railroad wants to free up the switches if there is no train on the approach circuit, they can add approach locking, which will immediately release the switches when the signal is canceled if no train is closely approaching the interlocking expecting to use the route that had been cleared.

If a train is delayed in the block, the rules require it to operate at restricted speed approaching any signals. This is required because the time locking might have expired, and the dispatcher might have moved one of the switches by accident.

>When, where and why do switches have timers?

Every power (dual control) switch should have a time lock, or rather the Control Point has them.

> Can a dispatcher override?

No. The purpose of the time lock is to prevent a dispatcher from making an error where he knocks down a signal then immediately throws a switch in front of an approaching train. Letting him override the time delay would defeat its primary purpose of safety.

>If a train is delayed in the block, the rules require it to operate at restricted speed approaching any signals.

OK so I'm nitpicking ;-) I assume you wrote that just to keep it simple as I often do that. But for those of you who like things exact... In CTC you do not have to operate at Restricted Speed after delayed in block on BNSF. You can operate at full track speed but must be prepared to stop at the next signal. Because as Run8 said, the dispatcher could have knocked it down, it timed out, and he re-aligned the switches or cleared a conflicting route while you were delayed.

>When, where and why do switches have timers?

When I read that I was not sure whether you were asking about the timers for interlocking/control point signals as described above or whether you were asking about ANY switch timers such as Electric Locked Switches have? In CTC territory many or most hand throw switches have electric time locks on them. A train that is in the clear and wants to enter the mainline at a hand throw switch must get authority to do so from the dispatcher and then operate the electric switch lock device. On these devices when you open the door they set all opposing signals to red. You have to operate a lever or push a button to start the timer timing down. After a preset time, often 6 to 8 minutes depending upon the track speed in the area and the signalling, the timer will time out and you can then manually throw the switch to enter the mainline.

If you are already on the mainline at the switch and wish to throw the switch (say to set out or pickup a car) you still have to open the timelock door and throw the lever but ours will let you line the switch immediately without a time delay in this situation. Some types won't, you still have to wait the time out. I believe that there are some types of these electric locks that the dispatchers can unlock? Ours don't operate that way.

Rules state that no train can clear the mainline in CTC at a hand throw switch that has no electric lock unless track speed is 20 mph or less at that location. That is because once you do that then there is no mechanically enforced protection to prevent you re-entering the mainline in front of a train.

Even siding switches have timers , they won't unlock till the run off time is gone or if a train is within about 25 feet of the switch.
This is to prevent someone from opening switch after a train is by last favorable signal before that switch.
Anyone remember the Jersey Macaroni factory incident.
The Mechanical lock once removed knocks down the signal, the electrical timer (little white light in switch mech, does not release the Switch till its known the block is clear.

Thanks for the very detailed answers.

The switches you are thinking of are anywhere on a signaled railroad where a train can enter the main line or controlled siding where the track speed is great than 15 mph. At least on the UP. Such as and industry spur or non-controlled siding. There is a timer on them that is activated by pushing a button or throwing a lever inside the lock box. At the moment the lever is thrown a track occupancy occurs causing red signals to be thrown up much like if there was a train where the switch was. You can't line the switch until the timer runs out to ensure that any train already beyond the previous signal and may have missed the light going red has time to reach and pass the switch. When the time runs out you can then line the switch. Newer and more expensive switch time locks have the capability to detect trains an may unlock immediately if none are around.


-p

Here's an example of a time lock used with a rigid manual switch stand in a typical mainline application. This is on the UP Valley Sub (former SP) in Turlock, CA. I don't have a shot of one with an open door but basically it has a lever inside and a white light that flashes while it times out and then goes solid when it's unlocked (IIRC...been awhile since I used one).

Mike

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"In CTC you do not have to operate at Restricted Speed after delayed in block on BNSF. You can operate at full track speed but must be prepared to stop at the next signal."

I do believe the BNSF Rules Department would not agree with the above statement.

Hoghead39 Wrote:
-------------------------------------------------------
> "In CTC you do not have to operate at Restricted
> Speed after delayed in block on BNSF. You can
> operate at full track speed but must be prepared
> to stop at the next signal."
>
> I do believe the BNSF Rules Department would not
> agree with the above statement.

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I don't know about the BNSF rules but here's what the NS rulebook says:

Rule 425 - "After a stop in TC or Remote Control territory, a train or engine not otherwise subject to slower speed must approach the next signal prepared to stop. EXCEPTION: At points where crews change, unless a leaving signal is provided, Restricted Speed must be observed until leading end of movement reaches the next signal."

Also, to expand on a previous comment, control point signals lined by a dispatcher will not time out - they can be lined hours ahead of time if conditions permit. The only signal I know of that will time out in CTC territory would be at an automatic interlocking.

>Hoghead39 said:
>I do believe the BNSF Rules Department would not agree with the above statement.

Sorry but I am certain that they do agree. That is the way it is.

Rule 9.9 Train Delayed Within a Block
B. CTC or Manual Interlocking Limits
Proceed prepared to stop at the next signal until the next signal is visible and that signal displays a
proceed indication.

That is all there is to it. Boogy. Now fuel conservation-wise they might not be too proud of you if you have a train and go to #8 to jackrabbit up to speed only to set the air and slow right back down again approaching the next signal, but it is legal by the operating rules. Light helper engines and my switch engine does it frequently.

>(NS) EXCEPTION: At points where crews change, unless a leaving signal is provided, Restricted Speed must be observed until leading end of movement reaches the next signal."

What? NS doesn't trust the inbound engineer to tell the outbound engineer what kind of signal they came in on?

>Also, to expand on a previous comment, control point signals lined by a dispatcher will not time out - they can be lined hours ahead of time if conditions permit.

When I was talking about "time out" (and I believe the others above too) I was refering to the "time out" or "timer run down" that must occur after a dispatcher knocks down a previously cleared signal before he can change any track switches or clear a conflicting route.

AAK Wrote:
-------------------------------------------------------
>
> >(NS) EXCEPTION: At points where crews change,
> unless a leaving signal is provided, Restricted
> Speed must be observed until leading end of
> movement reaches the next signal."
>
> What? NS doesn't trust the inbound engineer to
> tell the outbound engineer what kind of signal
> they came in on?
>

Nope, However I don't believe CR had this rule, as I've recrewed many a train in CR territory and had the hog-head say "we came in on a clear".

REflectiveMAN Wrote:
-------------------------------------------------------

> Nope, However I don't believe CR had this rule, as
> I've recrewed many a train in CR territory and had
> the hog-head say "we came in on a clear".

NORAC did have a delay in block rule, that stated the train must proceed at Restricting until:

1. A signal to proceed is clearly visible

and

2. The track between the train and that signal is known to be clear.

>NORAC did have a delay in block rule, that stated the train must proceed at Restricting until:

Was that for CTC or ABS or both? GCOR (BNSF) has different requirements depending upon whether its CTC or ABS.