# Can you really trip the crossing guards? **URL:** \ **Category:** Factual Questions\ **Created:** [January 17, 2006, 5:29am UTC](https://boards.straightdope.com/t/can-you-really-trip-the-crossing-guards/340326 "2006-01-17T05:29:21Z")\ **Posts on this page:** 7\ **Page:** 2
**Author:** ![Q.E.D](https://avatars.discourse-cdn.com/v4/letter/q/51bf81/32.png) [@Q.E.D](https://boards.straightdope.com/u/Q.E.D)\ **Post date:** [January 18, 2006, 3:24am UTC](https://boards.straightdope.com/t/can-you-really-trip-the-crossing-guards/340326/21 "2006-01-18T03:24:41Z")
> [@David Simmons](#): > > 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. Not necessarily. If the _entire_ section of track to each side of the grade crossing is electrically isolated from the rest of the track (and from each other, of course) as a track circuit up to, say, 1000 feet from the crossing, then any connection between the rails at any point will be read as a train entering that track circuit. Doesn’t matter if it’s 1000 feet away, or only 100 feet. See? ---
**Author:** ![minor7flat5](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/minor7flat5/32/258_2.png) [@minor7flat5](https://boards.straightdope.com/u/minor7flat5)\ **Post date:** [January 18, 2006, 3:32am UTC](https://boards.straightdope.com/t/can-you-really-trip-the-crossing-guards/340326/22 "2006-01-18T03:32:06Z")
> [@David Simmons](#): > > Because distances like 100’ for the sensor from the crossing are nonsense . . . 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. Sorry to be a pain about this **David** since your posts are always spot on and well intentioned. However, you are straight out calling me a lier here: I was not a child, neither was I drunk. I can recall the place where we did the deed. It may have been 50 feet; it may have been 200 feet. It was definitely not 1000 feet. As one other has stated, the fact that the detector is triggered by a train a quarter of a mile out does not mean one cannot trigger it right next to the signal. > [@TheLoadedDog](#): > > 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. We’re not talking about a single black box that sits at some predetermined point, we’re talking about a long conductive path, made up of rail, that runs from signal out to the boonies where the train should be detected. > [@Q.E.D.](#): > > Neat stuff, though. Looks like **David** and I still have a thing or two to learn, eh? ---
**Author:** ![Guinastasia](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/guinastasia/32/5751_2.png) [@Guinastasia](https://boards.straightdope.com/u/Guinastasia)\ **Post date:** [January 18, 2006, 3:42am UTC](https://boards.straightdope.com/t/can-you-really-trip-the-crossing-guards/340326/23 "2006-01-18T03:42:18Z")
> [@samclem](#): > > [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] I have to ask-in this day and age, could you be considered a terrorist suspect? ---
**Author:** ![spingears](https://avatars.discourse-cdn.com/v4/letter/s/ebca7d/32.png) [@spingears](https://boards.straightdope.com/u/spingears)\ **Post date:** [January 18, 2006, 3:52am UTC](https://boards.straightdope.com/t/can-you-really-trip-the-crossing-guards/340326/24 "2006-01-18T03:52:09Z")
> [@elbows](#): > > 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. It’s a lot easier to look for the insulated fish plates joining the rails. That’s where the action is. 😉 ---
**Author:** ![Kiwi\_Fruit](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/kiwi_fruit/32/12_2.png) [@Kiwi\_Fruit](https://boards.straightdope.com/u/Kiwi_Fruit)\ **Post date:** [January 18, 2006, 8:11pm UTC](https://boards.straightdope.com/t/can-you-really-trip-the-crossing-guards/340326/25 "2006-01-18T20:11:52Z")
People have metioned that the detection needs to be quite a long distance from the crossing so the barriers come down in time for fast trains. I can understand that. How is it that almost as soon as the last wagon of the train clears the crossing, the barriers start rising, or if there are only warning lights, they shut off? ---
**Author:** ![Ludovic](https://avatars.discourse-cdn.com/v4/letter/l/7ab992/32.png) [@Ludovic](https://boards.straightdope.com/u/Ludovic)\ **Post date:** [January 18, 2006, 9:27pm UTC](https://boards.straightdope.com/t/can-you-really-trip-the-crossing-guards/340326/26 "2006-01-18T21:27:44Z")
In fact, if it’s a matter of a simple current running through the rails, through the train or metal bar, then back to the detector, it may have been NECESSARY to be much closer than the train to use a homemade pseudotrain, as the real train’s resistance might be less due to greater volume of metal and greater area of metal in contact with the rail. Again, just because the detector’s parameters REQUIRED that it detect trains at a thousand feet or more doesnt mean it was required NOT TO detect them closer. ---
**Author:** ![TheLoadedDog](https://avatars.discourse-cdn.com/v4/letter/t/35a633/32.png) [@TheLoadedDog](https://boards.straightdope.com/u/TheLoadedDog)\ **Post date:** [January 18, 2006, 10:46pm UTC](https://boards.straightdope.com/t/can-you-really-trip-the-crossing-guards/340326/27 "2006-01-18T22:46:26Z")
> [@elbows](#): > > 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 ! **Adding to samclem’s warning: Part I** If you have actually done this - and it worked - it is extremely good that you ran off as fast as possible. Here’s why: by bridging both the insulated rail joins with pennies, you are _not_ closing the circuit that operates the crossing. Not directly anyway. What you are doing is making the relevant section of line twice as long by electrically connecting it to the adjacent section. This will not activate the crossing, unless the adjacent section is already occupied. By. A. Train. Once again, good that you ran off when you did. To the pranksters, this is even more dangerous than the crowbar. > [@springears](#): > > It’s a lot easier to look for the insulated fish plates joining the rails. > That’s where the action is. As has been explained previously, that’s just where the action _starts_. The crowbar will achieve the same effect from that point right down to the crossing and a little beyond. > [@Kiwi Fruit](#): > > People have metioned that the detection needs to be quite a long distance from the crossing so the barriers come down in time for fast trains. I can understand that. How is it that almost as soon as the last wagon of the train clears the crossing, the barriers start rising, or if there are only warning lights, they shut off? The crossing section ends shortly after the crossing (no reason for it not to, and plenty of reason for it to do so unless you want irate motorists). When the last wagon clears it, the section is clear, and the gates will open. Of course, the last wagon is the last wagon is the last wagon, so in this case the length of the train does not matter, as it does with an approaching train. The section break need only be a matter of feet away (unless it is a single track crossing). > [@Ludovic](#): > > In fact, if it’s a matter of a simple current running through the rails, through the train or metal bar, then back to the detector, it may have been NECESSARY to be much closer than the train to use a homemade pseudotrain, as the real train’s resistance might be less due to greater volume of metal and greater area of metal in contact with the rail. This is a good point, though it depends on where the rails are joined to the signalling system - it might not necessarily be at the crossing itself. As a case in point, Australian (And probably US) railways use what are called _Hi-Rail_ vehicles for maintenance and track gang transport. These tend to be road-registered Toyota 4WD vehicles (small SUVs). They are mechanically identical to the ones you or I could buy, with the exception that they have little flanged metal guide wheels which can be lowered into place for use on the tracks (they are quite humourous to see whizzing by). The steering is locked with a pin, and the rubber tyres still provide traction. When one of these is on the line, the signallers either have to book the entire line out of use to regular trains, or manually ‘block work’ the Toyota through the signals, section by section, with constant radio contact. The reason for this is that the little steel guide wheels are quite hit and miss with regards to their ability to close the signalling circuit, and can’t be relied upon to do so. So of course, weight and resistance plays an important role - not such a worry when you’ve got locomotives with thirty tons weight _per axle_, but a concern for the small fry. Which brings me to **Adding to samclem’s warning: Pt II** If you are silly enough to do the crowbar trick, and the crossing activates, don’t be too eager to slaps yourselves on the back and say, “Hey, it worked!” It might not have worked. Something else may have activated the crossing. Be prepared for the sickening sound of five-chime air horn approaching at 70mph. And when scramble for your lives, take the crowbar with you. They can derail a locomotive. [Previous page](https://boards.straightdope.com/t/can-you-really-trip-the-crossing-guards/340326.md?page=1)