My dad, very irresponsibly, explained to me one day that you can trip the crossing guards on railroads by connecting some piece of metal from one rail to the other. After years of wondering, my curiosity has gotten the best of me.
So, does that really work?
No. The rails of both tracks are already electrically bonded to one another, since they provide the Earth-return portion of the circuit for electric trains. The actual train sensors are usually electromagnetic, operating like metal detectors to sense when the train is approaching the grade crossing, as well as when it has passed. They can only be triggered by a very large mass of metal moving over them–I doubt if a prankster could generate a sufficiently strong signal to set them off.
Much as I hate to disagree with the esteemed QED,
I have actually done this, it does work, you need two people and two pennies.
You go back from where the crossing arm is to the first break in the rails, y’know where the two pieces but end to end. Once you’ve found this spot on each rail you both put your pennies down to span the gaps, but the arm won’t come down and the lights won’t flash until you both stand on the pennies.
I didn’t believe it would work either, I encourage you to get a friend and try it for yourself. Lights WILL flash, bells WILL ring, the arm WILL come down. And then you can run away like a drunken university student impressing her friends on the stumble home from the pub!
Enjoy !
And of course–the usual bar we used was the prybars that the “train guys” would leave in the nearby rail yard for moving empty traincars around. This was a heavy (1" diameter, 6-7 feet long solid) steel prybar with a square section on one end, bent at an angle and with a flat chisel end. You stick this under a train wheel and then pull on the end that’s up in the air (or–if you’re a little kid, you and two friends hang on the bar for a few seconds) and if the car’s brakes are released the traincar will s-l-o-w-l-y start to roll. The traincars were usually empty+open boxcars, sometimes empty flatbeds and empty coal hoppers.
…I don’t know if it was exacely safe for kids to be playing with this stuff, but where this all happened, it wasn’t really any sort of safety risk to passing trains because there was one well-used line that ran by a small rail yard that had a number of spurs on it, that led off to some factory buildings in a small industrioal center nearby. The train company would occasionally park empty cars on those spurs, and then put locks on all the switches. So at most you could only move an empty car a few hundred feet back and forth on one locked spur.
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There’s now a light-rail system in my area, it is even built on some of the previous diesel-rail lines. But you can’t go screwing aroud with it because they’ll put a Patriot act on your ass!
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Another clear YES (sorry Q.E.D.).
[stupidity]
A friend of mine from high school showed me how to do this. We found a piece of steel strap, the kind used to hold bundles of stuff together, and we took up positions on opposite rails about 100 feet from the crossing. We found that the best technique was for both of us to scrape at the rail with the edge of the strap.
After watching the crossing arms go down, we immediately went to Radio Shack and purchased alligator clips and wire to do this better. We went back to the crossing and clipped our long jumper wire across the rails, causing the crossing to close parmanently. We then went a distance away and waited until traffic began to build.
[/stupidity]
I can only wonder how many laws we broke doing that. We were messing with automobile traffic as well as train signals and the railroad, all likely covered under different laws, and all likely capable of sending us to the Big House for some time under the right circumstances.
And, I wasn’t being irresponsible. I used jumper cables. Only a very responsible person carries jumper cables with them.
Did you think I was lying?
I don’t suggest that you don’t try this, 'cuz as your grandmother told me “I won’t bail your ass out of jail, Buckwheat”.
Kids, don’t do this at home! Just wanted to say that you’re quite possibly looking at a Federal rap on the trespassing and interfering with the operation of a railroad. Local cops might want a piece of you for messing with traffic as well.
For some reason I came into this thread thinking it was going to be some kind of prank being played on the school crossing guard (like tying his/her shoelaces together while he wasn’t paying attention).
I’m kind of disappointed now.
By the way, in addition to messing with the automobile trafiic, you’ll probably delay a lot of trains also. Most modern railroads have automatic block signalling, and by connecting the two rails and tripping the crossing guard you are also making the signals think there is a train in that block, so no other train may enter that block.
There were workers at an old railroad shed/depot that has been converted to a workshop near my house and when they let metal rods hit the tracks the lights, bells and gate were activated.
I have to take those who claim to have done it at their word, I guess. However, they are lousy judges of distance when it comes to the distance from the crossing for the activators. Trains at one crossing I frequently use highball through there at about 70 mph. The gates take about 5 seconds to lower and they are fully lowered at least 10 seconds before the train crosses. So they activator has to be a couple thousand feet down the track. The distances they cite make do make me wonder.
Why would you think we are lousy judges of distance?
If there is a sensor that detects a short across the two continuous rails, why wouldn’t it work close to the signal? We walked to the signal and then walked a hundred or so feet down the track before we found the scraps of strapping we used. We wouldn’t have walked any further off the road than necessary.
I never doubted that the train with its many tons of steel and large number of contact points on the rail would make a far better short across the rails than we ever could, tripping the signal from a long way off. The rails themselves are not separate sectiions like in the old days; they lay them in long continuous seamless lengths. Thus, depending on the resistence of the steel rail, the train could be a pretty good distance away before the short tripped the signal.
I didn’t think you were lying. I just wanted confirmation. And that does sound like something Grandma E would say.
Thanks all!
Another clear ‘yes’, although I’m not going to say the system Q.E.D. describes is wrong, it’s just not the one with which I am familiar.
My city’s railway network operates electric trains running on a 1500V DC overhead catenary system, which of course, is grounded through the rails. The signalling system, on the other hand runs through those same rails, using low voltage AC power. For the purposes of the DC traction, the system cares not whether the rails are isolated from one another, but for the signalling system’s benefit, the rails are indeed electrically isolated (until, of course, a train enters the section and closes the gap).
Under this system, a reasonably solid crowbar should be sufficiently heavy to close the circuit and bring the gates down. It works for all signals, not just grade crossings. A crowbar across the track will fool the signallers into thinking that section is occupied, and the sections behind it will flip to ‘danger’, ‘caution’, ‘medium caution’, and ‘clear’, back for a couple of miles. So you can make a lot of commuters rather late for work by doing this. Then again, you’ll also get your arse handed to you by the police if you get caught.
If you look at the rail joins (especially on an electric railway), you will see heavy duty bonding cables across the gap and welded at either end, because the metal ‘fishplates’ which bolt the rails together can’t be trusted to provide an electrical connection. If you go to a road crossing, then walk down the line a way, you will see the rail join has no bonding cable, and the rails are bolted together through insulating material. This holds the crossing section electrically separate from the rest of the railway. How far away from the crossing this happens is dictated by the top speed of the fastest trains through the area, to give the last motorists time to get across and then give the boom gates time to lower - normally about 30 - 45 seconds.
As with all railway signalling practices, these things are failsafe. A circuit is required back to the signalling centre in order for the bom gates to be up and the warning bells off. There is always current flowing, and a train (or teenager’s crowbar) will simply short the circuit and no current flows to the central control. This means that if there is any fault of cut in power, the gates will lower.
[Moderator hat ON]
Just to add to what has been offered by some good people in this thread----
Do NOT rush out and try this. The world is a bit different than is was when many of us were kids and did stupid things. You just might find yourself in a world of hurt. What used to be just a kid’s prank might be interpreted today as a reason to lock you up or worse. Sometimes innocent sounding pranks result in people getting arrested or even shot.
I’ll leave the thread open for further points on topic. But let’s not be too creative on how to do this.
[/mod hat OFF]
Just to expand on my previous post - continuously welded rail (CWR) is increasingly used these days, but it is not universal. Even if it is used, they will still provide breaks in the rail for signalling purposes. On subways and commuter railways, the trains are light and have good braking, so they can make the sections shorter, and have the trains providing a high frequency service. On a freight railway, the gaps will be far apart. For the purposes of a road crossing though, this is all immaterial - theif there is no natural gap in the rails, the track laying crew will make one/ The distance from the crossing depends on the speed of the approaching train (note: it does not depend on braking ability in this case - if your car is stuck on a crossing, the train is not expected to be able to stop for you. You’re screwed).
The distance from the crossing that the section commences does not matter for our prankster pals. They can place the metal bar across the track right there at the crossing. No need to walk down the line.
Crossing gates and signals are operated by devices known as “presense detectors” which have evolved over the years.
At least some, at one time, COULD be tripped simply shorting between the rails.
If the crossing is in a location where a train may stop or move very slowly near an intersection, then a more complex type is used that factors in the speed of the train.
Locations near concentrations of teenagers with too much time on thier hands tend to get upgraded to more sophisticated equipment that is harder to spoof, but more expensive for the railroad.
My dad retired after 40yrs. as a ralway signalman. His job was to maintain, and at the end repair/calibrate/align such equipment. He worked for one of the smaller RRs in the US, and they had a few hundred signalmen to keep things working. I NEVER assume that the lights/gates will warn me of an approaching train.
Interesting. I’ve been doing some research and have learned about shunt-type track circuit signaling:
This is older technology that is being increasingly phased out in favor of newer systems, including computerized switching, sophisticated solid-state sensing and even GPS systems. Neat stuff, though. Looks like David and I still have a thing or two to learn, eh? 
It is interesting, indeed.
At the time, we didn’t consider anything more than that there was some current that would trigger the signal when we shorted the rails. After seeing what folks have posted here, it’s clear that we were short circuiting current that was necessary to keep the gates open, and that when the gates shut, some signals up and down the line must have turned red.
This explains one small detail of our shenanigans: After attaching the wire we quickly drove off. We gave a quick flyby ten minutes later to observe the results of our doing and were surprised to see an official-looking pickup truck parked nearby and some “train dudes” walking on the track. Though the signal was now working, we figured it would be imprudent to dilly dally any more. The mystery: How the hell did they get there so fast? In a time before pocket cell phones, nobody had time to call and complain about being stuck behind the gates.
Now it is clear: as soon as we did our funny business, lights blinked on on the “big board” in some darkened railroad control center. Some official railroad fellow then looked up at the blinking lights, noted that they were inconsistent with the rest of the track and figured a crowbar had just fallen from the sky on that section of track. He then called the boys to go find the problem.
Because distances like 100’ for the sensor from the crossing are nonsense. If you want to allow 5 seconds for the arm to swing down and 15 seconds before the train actually arrives at the crossing, 100’ would work for a train going less than 4 mph. For a train going 10 mph the sensor would need to be 293’ from the crossing. A train going 10 mph would be at the crossing 6.8 sec after passing a sensor only 100’ down the track.
In order for the guard system to work the sensor has to be at least far enough down the track to get the gate lowered before the train arrives.
Maybe those who have actually done it were all drunk or were small children at the time to whom 100’ seems like a long way.