Melvin Potts
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Railroad Crossing Signals

Tue Jul 18, 2006 4:11 am

Anyone know how these are activated?

That's someting I've wondered about for a long time.

Just what activates the signals..starts the bells ringing, lights flashing, and drops the gates?

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Trey
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Tue Jul 18, 2006 4:18 am

A sensor in the rails. When the train presses down on the sensor it activates the signals. Just like the Lionel 153C contactor put under a model railroad.

q2bman
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Tue Jul 18, 2006 4:42 am

Not exactly t-bolt. The sensor is an electric current in the rail sent out from the signal shanty in each direction for a long distance. At the end of the "distance" they place a canaster containing some electronic componants that "filter" the AC signal sent by the shanty. When an approaching "shunt" such as a train shorts the rail past the canister the computer in the shanty reads the speed at which the ac signal is being shunted towards the shanty. The computer calculates the speed the train is traveling and sends an activation signal to the relays that activate the crossing signal. The signal is set for a 30 second advance warning to the train entering the crossing. At the crossing the system has a "island" that activates the signals no matter what speed. The island is uaualy close to the crossing. Something like 15' either side. If an approaching train stopped prior to entering the island, the computer will sense the movement has stopped and allow the corssing system to turn off. Very complicated and awsome! The newer shanties house a computer with a fax line that will report false activations, malfunctions, and lots of other stuff. The older versions are just voltage goig to the canister that activates as soo as the train passes it. Neat system though. You realy should take a peek inside if you get a chance. Very complicated for some red flashy lights!!

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Trey
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Tue Jul 18, 2006 4:51 am

q2bman wrote:Not exactly t-bolt. The sensor is an electric current in the rail sent out from the signal shanty in each direction for a long distance. At the end of the "distance" they place a canaster containing some electronic componants that "filter" the AC signal sent by the shanty. When an approaching "shunt" such as a train shorts the rail past the canister the computer in the shanty reads the speed at which the ac signal is being shunted towards the shanty. The computer calculates the speed the train is traveling and sends an activation signal to the relays that activate the crossing signal. The signal is set for a 30 second advance warning to the train entering the crossing. At the crossing the system has a "island" that activates the signals no matter what speed. The island is uaualy close to the crossing. Something like 15' either side. If an approaching train stopped prior to entering the island, the computer will sense the movement has stopped and allow the corssing system to turn off. Very complicated and awsome! The newer shanties house a computer with a fax line that will report false activations, malfunctions, and lots of other stuff. The older versions are just voltage goig to the canister that activates as soo as the train passes it. Neat system though. You realy should take a peek inside if you get a chance. Very complicated for some red flashy lights!!
I wasn't just overly sure so my bad. :oops: I agree with you q2bman its alot of electronics for fourteen flashing lights, two bells, and two gates on a standard crossing.
Its very good to hear that in the newer signal controls will "fax in" a malfunction report. We've had a crossing down here that when they worked on the railroad track, they would remain in operation after the train passed...I was the only one to call in reports. :roll: Did it about a week or two...every night! :shock:

q2bman
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Wed Jul 19, 2006 12:24 am

The older cabinets have a more simple design that is prone to malfunction. The new stuff still breaks down but is less likely to do so. Also the battery back up seems better. Not a metal box in the ground!
I had a crossing in my home town that would activate, train would pass, deactivate, then when the train passeed main st and the gates went up it would activate again and then go off after about 5 mins! Messed up!

Jim_Ferer
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Wed Jul 19, 2006 1:53 am

Rails are often broken up into sections electrically isolated from one another by insulated joints. You'll see a slightly odd looking joint fished between two sections of rail, usually painted a contrasting color. Of course there's a small gap between sections of rail. You're most likely to see this in mass transit or commuter rail.

Signals used to be activated by switches that the train ran over and pushed down, just like a track greaser works. A lot of these are still in service. Heck, the New York City subway system still has electromechanical signals. My company did a contract and went through hell trying to replace the relays, some of them with clockwork delays and all sorts of weird stuff. Contractors are required to hire a TA retiree signalman to supervise; nobody else has any idea how to work on 'em. The TA is trying to modernize the system but it isn't easy for a signalling system that's been in service a hundred years and will cost $2 billion or more to replace.

Crossing signals placement and so on are regulated by the Manual of Uniform Traffic Control Devices (MUTCD). Design specifications are in the AREA manual (American Railway Engineering Association).

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Sun Jul 23, 2006 8:38 pm

yeah here in Brookings (south dakota) they just did a light upgrade to LEDs, & on a lower note all the traffic signal lights are getting LED upgrades. Its known as Project LED

Robert Gift
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mee-mool lights activation

Wed Aug 09, 2006 7:45 am

In Lewistown, PA, in late 50s, as a little boy I asked my grandfather what turned on the "Mee-Mool" lights.
Pup-pup said the weight of the train squeezed the "juice" out of the rails.
So, I started piling ballast rocks on the rails, then finally thought to stand on a rail since I weighed much more than the rocks.
Nothing.

Later, I walked along the track and noticed all rail joints were electrically connected with cables until one joint was insulated with almost half inch thick of paper-appearing insulation several hundred feet from the crossing.

On a hunch, I found a piece of metal, wedged it between joints of right and left rails. This was part of a small "Yard" that was used only during weekdays.
First I removed oxidation by rubbing the metal strapping with a piece of ballast rock.
The crossing signals activated!
There were no bells on crossing signals without gates back then, so no commotion.
Also, the street crossing that section of track had almost no traffic.

I left and returned a half hour later expecting someone from the
PRR to have pulled out the metal.

Nope. Crossing signals were not indicated on anyone's electrical panel.

I walked back to the scene of the crime (and it IS a criminal offense!) and pretended to trip on this wire across the track and pull it out.

A weekday I watched a train enter that insulated section. It was moving VERY slowly and the signals were activated 2 minutes before it finally arrived at the crossing.

Now, I presume they have motion detection so the signals activate only
25 seconds before train arrival at the crossing no matter what the speed.

What is meaning of Karma # and all the little numbers on these posts?

Thank you,

q2bman
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Thu Aug 10, 2006 3:18 pm

The new signlas will still activate from about 25 ft from the road even today instantly. Its called the "island".

Anyway, ya its a bigtime crime to the RR Police. They will arrest you.

And the #'s on the posts are mile post locations. It's how the trains tell the dispatcher where they are and how they get authority to move in non signaled track teritory.

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quiksmith10
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Thu Aug 10, 2006 5:59 pm

[quote="q2bman"]The new signlas will still activate from about 25 ft from the road even today instantly."

There isn't a set "distance" on where crossing lights and guards are activated. It depends on the speed of the tracks in the area and any type of sight blocking obstacle (ie, a curve). The higher the speed, the longer the distance the activation point will be placed. 25 feet is a very close distance for an activation point. The train would be to the crossing before the gates (if there were any) would be down. Usually the activation point is a couple hundred feet down the tracks, if not more.
Brandon Smith

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