How Railroad Crossing Signals Work

hello again rail fans a question that i've been getting frequently recently for some reason is about railroad grade crossing signals automatic signal activations how do they work how does the signal know when the train is there how does it know when the train is gone well i'm going to give you the simple answer to this because frankly it's the only one i got a long time ago railroad engineers discovered that they already had the means for automatic activation of those devices in those two steel rails they realized that if they put an electric current up one of the rails and then sent it back down the other rail that they had the means for the automatic activation right there when the train came along with its steel wheels and axle and bridge those two rails bridging that current it created a switch that could activate a device and so the automatic grade crossing device was born it was probably i don't know this for sure but it was probably thomas edison and or george westinghouse that had a hand in that they were the bill gates and elon musks of their day now those were the early versions the very simple versions in the decades and decades since then the devices have gotten much more sophisticated but let's start with those those simple devices one of the oldest and most basic type of crossing signal activations still in use is the approach island system here at the county line sperm near lakeland florida this local is crossing u.s highway 92. he was already on the crossing when i got there but you can still see how this works it's a conventional track circuit system of the most basic design it doesn't even have approach circuits because it really doesn't need them trains always back into this spur because it's a dead end down there so they're always going 10 miles an hour or less not much approach time needed the train simply pulls up to the crossing and stops while the signals activate when the gates go down they move on across folks often speculate that it's some kind of weight sensor or seismic detector that triggers the signals but it's far simpler than that the steel wheels and axle actually bridge the rails and complete an electric circuit in this example that insulated joiner bar with the white paint actually begins the island circuit of the crossing when the first set of wheels hit that the signals activate the island circuit is that stretch of rail which goes across the roadway it's called that because the approach circuits extend way out from the crossing on either side and the island circuit is in the middle hence the name across the road another insulated joint ends the circuit watch as the front wheel of the locomotive clears the electric contacts on the far side almost the instant he gets off that small island circuit the gates come up and the lights go off again this is a conventional track circuit and is the oldest and most basic type of crossing activation system much newer technology includes the motion detector at hawthorne florida on csx's s line the johnson street crossing is a motion detector system when the train passes into the detector circuit the wheels shunt the two rails and begin changing the impedance of a coded circuit in the track the electronics and the signal box trigger the crossing lights and bells as the train gets closer the impedance keeps changing letting the software in the signal box know that the train is coming toward the crossing and to keep flashing and ringing if q453 were to stop before the crossing the motion detector would sense that the track impedance stopped changing and after a number of seconds it would turn off the signals the federal highway administration recommends a 20-second lead time for signals to activate before the train arrives but it's common practice to set crossing circuits at 30 seconds this particular installation is set for 45 mile an hour trains track speed through here but 453 isn't running more than about 25 so the lights activated 56 seconds in advance of the train but johnson street is clearly not a busy crossing so no problem [Applause] an improvement to the motion detector is the speed predictor this is firmware that takes the motion detector information and uses it to calculate the speed of the approaching training with this system the speed of the train doesn't matter the predictor begins figuring that speed versus the length of the circuit and produces a trigger time that's roughly 30 seconds to the crossing at magnolia street in ocala q453 activated the crossing signals and hit the pavement 32 seconds later next we'll look at the motion detector and how it keeps highway traffic moving the advantage of the motion detector system is illustrated in this shot i caught in rebecca georgia the northbound freight is in the siding waiting for an approaching southbound he's pulled up just short of the highway crossing in a few seconds the motion detector senses he's not moving and deactivates the crossing signals this saves a lot of anger from drivers trying to get across at deerfield beach florida on the x seaboard main line into miami is an excellent example of the speed predictor and motion detector at work the deerfield station is right next to a big crossing hillsborough boulevard is six lanes in each direction lots of traffic crossing signal connections to the track are well marked with that orange paint so we can see where they are as we look way down south we see a clear signal on the number one track at parker crossover there's a southbound somewhere in the block at 8 37 a.m tri-rail arrives triggering the signals one minute before it hits the crossing the four quadrant gates are fully lowered 32 seconds before he's on the crossing tri-rail is commuter service between the miami airport and mangonia park in west palm beach now watch as he clears the roadway less than four seconds off the island circuit and the gates start coming up even though he's clearly still on the southern approach circuit the signals don't care because this side was disengaged when the train hit the northern approach circuit first it works the same for trains going either way at 0.906 amtrak 98 appears from the south he originates at hialeah yard in miami and runs to new york city he's rolling down into his third stop on that journey deerfield beach in a move that's been measured and perfected the silver meteor glides down to a stop just before he gets on the hillsborough boulevard crossing circuit they rely on the motion detector to go to work here when amtrak 98 stops rolling the impedance of the coated signal in the rails stopped changing the motion detector is set up to process this and after a number of seconds it begins shutting off the crossing signals so drivers won't become irate while the train is standing in the station south florida is a busy territory and blocking a roadway like hillsborough boulevard for even five minutes can cause big problems it takes a few minutes on this sunday morning to get everybody on board but when the engineer gets the depart order from the conductor he uses his dtmf keypad to transmit a set of tones on the radio that reactivates the crossing lines this avoids the need of having to play chicken with the automatic crossing system by rolling up slowly on the highway hoping for an activation it doesn't always work soon enough when a train is this close today 98 has a ge-8 locomotive dead in tow one of the few that amtrak still owns i thought it was brought to hialeah for servicing from somewhere up north but i'm only guessing at that all this algebra and decision making happens in the little silver houses you see next to crossings commonly called signal bungalows these structures hold all the electronics that control each crossing they even house backup batteries to keep the signals working through a power failure traditionally these batteries lived outside in concrete boxes next to the bungalows back when they were older lead acid type it's all in one house now at gay road in lakeland there are no crossing signals in fact the crossing was closed a few years ago but i'm here on this bright day before st patrick's day 2021 because q453 is showing off some special power the 3194 is csx's spirit of law enforcement engine the es44ah honors police fire and emts in a blazing blue black and white design at mid-train actually toward the bottom end was a distributed power unit another csx spirit locomotive the 911 is also an es44ah and also honors first responders but with a decidedly more firefighter design today's 453 has the usual miscellaneous traffic on top and auto racks on the bottom 453 is on track number one the southbound number two track signal has gone to approach proceed prepared to stop at the next signal ahead that's for o710 a local moving down to work customers at plant city he's getting the approach signal because 453 is on the crossover switch and the siding switch at winston pass which is the next signal ahead 0710 will pull to the south end and tuck in there until q453 clears up which will be quite a few minutes this morning he's making a move called pulling by and backing in that means just what he says pulling past the entire winston y plant then backing his entire train 9 600 feet of it around the south leg of the y and into winston yard i move around to the stem of the winston y where 453 will be coming in old tampa highway is listed as a conventional crossing circuit with an approach island approach set up ah come around this curve the signals activate 52 seconds before he arrives at the crossing because this kind of setup doesn't know how fast he's moving it simply turns on when he covers the approach circuit and stays on until he's clear of the island circuit that's the rails in the crossing and a few feet out either side all right thirty more oh at this point he's stopping because the conductor way down on the bottom of this 9600 foot train has to line a yard switch before they shove all the way in takes about a minute and a half while 453 is stopped on the crossing the signals stay activated as long as he's on that island circuit in the roadway the lights will flash and the gates will stay down those white chalk drawings on cars aren't graffiti it's message art usually from car inspectors to one another in different terminals my dear departed friend crick hatch in folkestone georgia first told me about this messaging he had hundreds of photos of this stuff apparently the practice is still alive and well this is not message art it's tagger graffiti much less talent involved here 453 gets rolling again and we get one more look at that lead engine when he clears the pavement that conventional crossing circuit doesn't give me much time to ski daddle almost the second he's off the island circuit the gates start coming up and those drivers aren't waiting for me [Applause] well that's the simplified version of how railroad grade crossing signals are activated i hope that answered some of your questions there's much more detail to how these things work it involves microprocessors and special sensors and positive train control but um those uh that we did here today are kind of the basics please hit the like button if you like this video subscribe to the channel if you haven't already done that hit the bell down there to be notified when i do post a new video write your comments in the comments section below i try to read all those and i reply to as many as i can same with the email email me at railfandanny gmail.com read every one of those and reply to as many of those as i can so let's plan to meet up again somewhere soon somewhere out there on the high iron and until we do this is danny harmon out

Channel: Distant Signal

Views: 291,308

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Id: 4qdti3atxpw

Length: 16min 49sec (1009 seconds)

Published: Fri Mar 26 2021