🚀 go-pugleaf

> 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.

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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...