(continuation of the switch discussion)
Time lock switches
Time lock switches are manual switches found in t-rail on the mainline. Like all other mainline t-rail switches, they are padlocked for safety. However, these have an additional lock built in where the switch can’t be thrown until a timer has counted down, hence the name. They will have a sight glass on the switch machine that displays the status of the lock – it’ll show the word padlocked, which is what will be there under normal operating conditions while the padlock is in place; locked – which is that status after the padlock was removed but before the timer is up; and unlocked, meaning that the padlock has been removed and the timer has run out, so the switch can now be thrown.
Time lock switches on the alignment (except Interstate)
If there is no train detected in the approach circuit where the switch is, the timer takes 17 seconds before the switch can be thrown, and this will throw up reds on all the ABS signals around it to prevent a train from entering the circuit.
As an example, the switch to enter the Hollywood pocket track (located between the Hollywood platform and the NE 60th platform) from the westbound mainline is a time lock switch. A westbound train can leave the NE 60th platform on a green and generally speaking will expect to see a yellow on signal 46, which is the intermediate ABS signal in between the platforms at 60th and Hollywood – remember how ABS signals work:
When a train leaves 60th on a green, it’s clear to proceed for 2 ABS blocks, meaning that the intermediate signal should be yellow (which tells you that you’re clear to proceed into the Hollywood platform). However, if the switch for the pocket track is thrown after the train leaves 60th, the intermediate signal 46 will not be the expected yellow – it will be red to prevent the westbound train from entering the circuit after it. This is why operators can’t run on autopilot and just assume what their signals will be!
If there is a train in the circuit approaching a time lock switch, it takes 4 minutes and 17 seconds before the time lock timer runs out and the switch can be thrown – this is done as a safeguard to give the train time to get out of the circuit before the switch is thrown.
So if you’ve ever wondered why the Red Line trains in the center track at Beaverton can’t keep going west… well, they technically can, but those switches immediately west of BTC from the pocket track that the Red Line sits in are time lock switches that will take 4 minutes and 17 seconds to throw if you’ve got a Red Line in that circuit.
Basically, it’s not practical to send a train through here because of how long it would tie up mainline traffic. But it can be done when necessary, as happened recently when a broken train in the westbound main at BTC necessitated the use of the time lock switches to get a train around it to continue west (I wasn’t near BTC when that happened, and so many thanks to EMS for sharing these on-the-scene pics)
Time Lock Switches on Interstate
These work a little bit differently – first, the timer on the Interstate time lock switches takes 60 seconds to count down. And unlike the other time lock switches, the timer doesn’t start once the padlock is removed – because of the way Interstate is set up, Control will run the timer.
So, that brings us to Matt’s & pdx77’s questions (I’ll just cut and paste as Matt wrote them to respond):
What are the Lunar/Red signals along Interstate Ave. for?
This question refers to this “signal” (and others like it) located on Interstate Avenue. It’s actually not a lunar and red signal – the only other thing it can display is a yellow X which you can sort of see here, but that’s pretty rare.
Do you the locations of them and the numbers of them?
There are four of them – 421 located at the northern edge of the N Prescott St platform and 423 located near the pedestrian crossing at N Sumner. Then further north, there is 427 near the N Lombard platform and 429 near N Winchell St.
I also noticed that all of the other signals on the system are even-numbered but these ones are odd-numbered..do you know why? I have also noticed that they don’t have an “N” before the number..is there also any reason for that?
These aren’t signals like the ABS or combination signals – as I mentioned before, these are called summary switch indicators or also advanced switch indicators (so that’s why they’re not numbered the same way the signals on Interstate are because they are not signals in the same sense of the word).
These indicators are associated with switches at the crossovers on the Yellow Line Interstate alignment.
And similarly, indicator 423 is associated with switch 423A & B, and indicators 427 and 429 are associated with switches 427A & B and 429A & B.
As you might have guessed, these switches are all time lock switches. For safety, once the padlock of one of those switches on Interstate is removed, the summary switch indicator will display a yellow X instead of a lunar.
Any train that approaches a summary switch indicator with a yellow X MUST stop and call Control for permission to proceed – it doesn’t mean that the switch has necessarily been thrown, but it does mean that the lock has been removed and that’s reason enough to require permission from Control before continuing.
The setup here is different because unlike the time lock switches found elsewhere in the alignment that are protected by ABS signals, Interstate is in pre-empt territory.
Other point of interest – as I’d said before, emergency vehicles can drive over the rails on Interstate because it’s embedded in the pavement. But it’s t-rail, not girder rail, and so the switches aren’t going to be embedded. So these orange reflectors that surround the crossover switches on Interstate let emergency vehicles know they need to clear out of the tracks before they get to the reflectors since they can’t drive over the switches.