🚀 go-pugleaf

In article <1h4r8rINNjsu@hp-col.col.hp.com> cab@col.hp.com (Chris Best) writes:
>> The old style worked by detecting a short circuit between the rails 
>> (a locomotive is pretty conductive). If you walk the track near a
>> crossing and pay attention to where the rail ends meet, you will see
>> that some are electrically connected and some are isolated. You will
>> also find cables connected to the rails running under-ground toward
>> a nearby electrical box which controls the whole thing.

>Indeed, the old style worked by shorting the rails.  Used to be, you
>could connect the rails together with jumper cables, and the gates
>would activate, or a nearby block signal would turn green (trust me).
>
>That was in my childhood - but not long ago, I tried the same thing 
>near a protected crossing, and nothing happened.  At the time, I just
>figured that the equipment was smarter, and knew better than to
>respond to a "train" that just appeared on a block without being on
>an adjacent block first.

>So I had that part right, but I don't see why they'd change the
>sensing scheme - just the interpreting curcuitry.  But if the
>guy who "drives the big trains" sez so, I guess it's so...


'Cause if the train is going fast, the gates go down, in 30 seconds the
train comes, it clears the crossing and the gates open.  If the train
goes slow, the gates go down, the train doesn't show up for 2 minutes
and the impatient drivers go around the gates.  Eventually, one of them
gets hit.  The new sensing scheme allows the gates to close x seconds
before the train gets to the crossing rather than when the train is y
feet away.  Reduces the risk of hitting a motorist.