Timers and Wheel Detectors

[Ethan777]

I'm quite intrigued by your timer system in your signalling. Other than CBTC, the subway uses fixed block signalling right? Well dont the trains receive speed codes for the TOs to follow rather than use timers to regulate speed? But I heard the trains here dont have in-cab signalling. Or are timers some additional safety feature to the signalling system exclusive to NYC subway only? When are where were they first implemented? I wonder if my perception of how timers work are correct:

 

TOs know that they going to pass a timer once they see a GT or ST sign and thus slow down to the speed as printed on the sign. There are timers that give u 1 chance or 2 chances to clear. Its about presetting the signal to show a clear aspect after a fixed amt of time from the point a train is detected in a block. The time given is pre-determined by how long a train takes go pass a certain section at a certain speed and that if they reach the signals faster than the preset time the signal assumes the train is going too fast and makes it trip the arm to stop it. But do engineers add a few seconds more to this preset time to cater to small allowances in train speed or that whatever they calculate before hand is just set as accordingly? Does anyone in here know the exact time preset for all the timers across the subway? Typically, How much time is given?

 

So a 'stopwatch' in the signal starts once a train enters a traffic block and after the preset time, the trip arm retracts and the signal turns green and the S disappears. For one shot timer, its only one try to clear while for two shot timer, the first barrier wont have a trip arm but will have a signal to let TO know if they have cleared the first timer then the second signal will have both trip arm and signal ready to trip a train if its going too fast.

 

For station timers, its basically to allow the back train to inch up to the front one at a station so long as its under the GT speed prescribed. If the train is inching to the front one too fast, the signal just before the platform will trip it before any collision?

 

When I was in NYC last June, i wasnt able to notice a timer. All the signals looked the same to me. Is one characteristic of a timer include having the S light at the bottom? What other characteristics are there to tell from a normal signal and timer signal? Are timers compatible on CBTC-ed lines?

 

For wheel detectors, are they supposed to work in hand with timers? Basically the driver must slow down to the prescribed speed before passing the signal that has the WD light if not he will be tripped. Again, is this something thats exclusive to the subways? When and where were they first implemented?

 

I know there's a guide on this on nycsubway.org but i still dont quite understand how it works after reading it multiple. So, hope i can clarify my doubts here

[Fresh Pond]

You won't always find a white S on timers. Sometimes it'll be a white light at the bottom of the signal, a white D, or a number instead (be it 10, 15, 20, 25, or 30).

 

As for wheel detectors, they're like another form of timers. If nothing is flashing, then it's off. If it's blinking, you have to slow down to the posted speed or get tripped. A steady light means you're at the right speed

[Ethan777]

When i was at South Ferry last june, i thought i remembered seeing many 'S' lights together in one signal at the front of the Outer Loop. Having multiple 'S' doesnt mean anything right?

[SubwayGuy]

Answers in red.

I'm quite intrigued by your timer system in your signalling. Other than CBTC, the subway uses fixed block signalling right?  Yes Well dont the trains receive speed codes for the TOs to follow rather than use timers to regulate speed? No, except on the L line which uses "CBTC - Communication Based Train Control" signalling, but the speed codes only apply when the TO is operating the train in Manual mode. When the train is in ATO - Automatic Train Operation - it operates itself. But I heard the trains here dont have in-cab signalling. Subway trains don't. Metro North and Long Island Railroad Trains do, to varying degrees. Or are timers some additional safety feature to the signalling system exclusive to NYC subway only? When are where were they first implemented? I wonder if my perception of how timers work are correct:

TOs know that they going to pass a timer once they see a GT or ST sign and thus slow down to the speed as printed on the sign. There are timers that give u 1 chance or 2 chances to clear. Its about presetting the signal to show a clear aspect after a fixed amt of time from the point a train is detected in a block. The time given is pre-determined by how long a train takes go pass a certain section at a certain speed and that if they reach the signals faster than the preset time the signal assumes the train is going too fast and makes it trip the arm to stop it. This is correct. But do engineers add a few seconds more to this preset time to cater to small allowances in train speed or that whatever they calculate before hand is just set as accordingly? It depends on the location. Any Train Operator knows to respect Grade Timers and not challenge them. Does anyone in here know the exact time preset for all the timers across the subway? Typically, How much time is given? Again, it depends on the location. A GT35 signal 1,000 feet from the GT sign will have a very different time value than a GT15 signal the same distance from its GT sign.

So a 'stopwatch' in the signal starts once a train enters a traffic block and after the preset time, the trip arm retracts and the signal turns green and the S disappears. For one shot timer, its only one try to clear while for two shot timer, the first barrier wont have a trip arm but will have a signal to let TO know if they have cleared the first timer then the second signal will have both trip arm and signal ready to trip a train if its going too fast. Pretty much.

For station timers, its basically to allow the back train to inch up to the front one at a station so long as its under the GT speed prescribed. If the train is inching to the front one too fast, the signal just before the platform will trip it before any collision? Yes, with one correction "its basically to allow the back train to inch up to the front one approaching a station so long as it's under the ST speed prescribed." Station Time values are calculated to ensure safety - thus a train travelling at maximum speed will be placed in emergency if it hits a red signal well before the train ahead of it. Whereas a train that has demonstrated (by clearing the station timers) safe speed will be allowed much closer to its leader, however, if it randomly speeds up after clearing the first station timer, it will still be stopped before it can collide with the first train since it will be travelling at a much slower rate of speed having had to slow down to clear the station timer. Regardless, at all times, there will be at least 2 red signals protecting the train in front of it.

When I was in NYC last June, i wasnt able to notice a timer. All the signals looked the same to me. Is one characteristic of a timer include having the S light at the bottom? What other characteristics are there to tell from a normal signal and timer signal? Are timers compatible on CBTC-ed lines?

 

S or D light, or a "lunar white" which is a bluish-white light on the bottom of the signal. Station time can be indicated by an illuminated plate with the prescribed speed on it, so for ST15, a white "15" will light up on the red signal. Timers are not compatible with CBTC. If a speed restriction is to be enforced with CBTC, it is programmed into the route and the train is simply not to exceed it. Where fixed signals are used with CBTC (and the train AND its predecessor are both operating in CBTC), the only signal aspect displayed will be flashing green.

For wheel detectors, are they supposed to work in hand with timers? Basically the driver must slow down to the prescribed speed before passing the signal that has the WD light if not he will be tripped. Again, is this something thats exclusive to the subways? When and where were they first implemented?

 

Wheel detectors go above and beyond timers, and are only used over (or approaching) switches. They were installed in the 1990s after the 14th St. Union Square wreck on the #4 line. They are only in effect when the switch is set to cross the train, or when no route has been established at the switch. They use wheel detection points which measure the speed of the individual wheels by timing them over a very close distance. If the train's speed exceeds the limit, the wheel detector places a stop arm up underneath the train, which will put the train in emergency. Therefore a train in a wheel detector area must maintain the appropriate speed (which is almost always less than what's posted) throughout the entire wheel detector area. A sign indicates when the train is clear of the wheel detectors.

I know there's a guide on this on nycsubway.org but i still dont quite understand how it works after reading it multiple. So, hope i can clarify my doubts here

When i was at South Ferry last june, i thought i remembered seeing many 'S' lights together in one signal at the front of the Outer Loop. Having multiple 'S' doesnt mean anything right?

 

If they were painted on a fixed sign, that's the stop marker for the train, not a timer. The S or D must appear on a signal to be associated with grade time.

[GreeneggsnPelham]

Couldn't have said it better myself! It's always fun to see someone else as interested in timers/signals/etc as I am.

 

-A 

[Kamen Rider]

Ethan, you need to consider the following

 

#1. The subway is OLD. In function, if you consider the age of the entire network and it's constituent parts, it is the second oldest rapid transit network in the world. The Gates Ave Station on the J line, about a mile and a half from my house, has been in day to day rapid transit service since May 13th, 1885. That would make it the oldest purpose built rapid transit station in the world outside London still in service. The section of the line, while partly rebuilt, out eastward to Van Siclen Ave opened in phases by the end of that year. The vast majority of the network was built in the next 50 years, done even before the US entered World War II.

 

#2. The city suffered an economic collapse in the 1970s as the middle class fled to Long Island and New Jersey. This lasted into the 1980s. The city was a nightmare. Dirty, dangerous, and basically dying. People were counting the days for Los Angleses to surpass it as the largest and most important city in the country. In that time, the there was no money of capitol work, nothing got upgraded. Between the opening of the Christie Street connection in 1967/1968 (which brought with it Grand St and 57th st/6th Ave Stations and the 6th Avenue express tracks south of 34th street) and the opening of the Archer Ave line in 1988, not one inch of new line was opened. 

 

They could not afford to install anything new and fancy if they had to spend all their time, money and energy on fixing everything that was already there. It's only with the upswing of the 1990s that there is money to install the new signal system and expand the network. 

 

#3. The size and costs. The subway has 656 miles of track in passenger service, making up 232 route miles. Most of these track miles are open all day every day, and closing them to replace the signal system is a nightmare, just ask anyone who lives along the L and the 7. the L was out so much for the upgrade, CBTC was jokingly said to actually stand for "Catch the Bus to Canarsie". They have yet to test the CBTC system on a 4 track mainline. the L is 2 tracks the whole way, the 7 is 2 from 34th street to Queensboro Plaza and 3 past there to Main Street.