Ask fellow member Brandon O How they work or don't work
Modern Tech One step forward and two or more back
sjh
----- Original Message -----
From: "Russell Strodtz" <vlbg@earthlink.net>
To: <BRHSlist@yahoogroups.com>
Sent: Saturday, October 11, 2003 9:31 AM
Subject: Re: [BRHSlist] How does a railroad crossing work?
> There are a number of different technologies applied to the
> activation of grade crossing protection.
>
> The simplest ones just put the gates down when ever there is an
> occupancy in a certain section of track approaching the crossing.
>
> There are newer and fancier devices that will give exactly 36
> seconds from activation to train arrival. IIRC that is the FRA
> standard.
>
> The gates go up because the approaching train has cleared the
> crossing.
>
> The gates go up when a train stops short of the crossing because
> the circuitry has a timing function that can detect that there has
> been no movement.
>
> At some locations there is a feature that allows someone with a
> switch key to put it into a slot in a metal box and activate the
> crossing. For quite obvious reasons I have never heard of any
> location where the same function will deactivate the crossing
> protection.
>
> Think of the track at the crossing as divided into three sections:
> An approach from the North.
> An "island" right at the crossing.
> An approach from the South.
>
> In the simple systems the crossing is activated as soon as a train
> occupies either one of the approaches. When it clears the island
> the activation is ended.
>
> On the motion sensing systems the hardware and software is looking
> in both directions all the time. When a train enters either approach
> it completes an electrical loop. As it gets closer the loop gets shorter.
> The motion sensor can calculate the rate of change and adjust to that
> 36 second number at any train speed. If the train stops there is no
> longer any rate of change and after a little while it will turn off the
> activation. When the train starts moving again the rate of change will
> start again and the crossing is activated. Motion sensors generally do
> not use islands. Don't need to. If the electronics can detect an
> approaching train and calculate it's speed then they can also detect a
> train moving away from the crossing by a reciprocal rate of change.
>
> If there are no insulated joints at both sides of a crossing it usually
> means it has a motion sensor and does not need an island.
>
> If the trackage involved is signaled the signal system and the crossing
> protection coexist by using different frequencies and filters.
> ----- Original Message -----
> From: "wollffee" <wolfee@onebox.com>
> To: <BRHSlist@yahoogroups.com>
> Sent: Saturday, 11 October, 2003 08:39
> Subject: [BRHSlist] How does a railroad crossing work?
>
>
> > What triggers the lights/bell/crossing gate when a train approaches
> > the crossing? How come when the BNSF approaches the crossing at 80th
> > and Sheridan, NW of Denver, it triggers the crossing a quarter mile
> > before it gets there--even a coal train chugging at 5 mph. But, once
> > it passes, the gate goes up almost instantly after the train is
> > thru? Sometimes a southbound pulls right up to the crossing and then
> > stops. After he gets stopped, somebody does something to let the
> > gate back up while the train just sits there. How do they make the
> > gate go back up when the train is parked just a few feet from the
> > crossing?
> >
> >
> >
> >
> >
> > Your use of Yahoo! Groups is subject to
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> >
> >
> >
>
>
>
>
>
> Your use of Yahoo! Groups is subject to http://docs.yahoo.com/info/terms/
>
>
>
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