>Hi,
>I was wondering how most automated level crossings work, ie what trigers
>the lights to start flashing (and for that matter, signals)? Is it, as I've
>always thought, a circuit which the train makes thereby starting the
>operation of the flashing lights (ie a section of track before the level
>crossing is insulated from the rest of the track, and when the train
>crosses into it, it causes a small current to flow between the rails)?
>Are there a variety of ways to trigger level crossing lights and signals?
>What are they?
>Many Thanks!
>--
>Adam Joyce
>9706360s@magpie.magill.unisa.edu.au
>(When replying by e-mail please remove "NoSpam_" from e-mail address)
Your pretty close, although its a little more complicated depending on whether
the level crossing is on single , double or bi directional signalled track.
There sometimes can be two approach track circuits , used to differentiate
between high speed trains and slow freights, so as to get the lights to start
without traffic having to wait long periods of time.
The crossing can also be interlocked with signals so that the lights wont
start flashing if the signals are red, a common situation on single line
track where there is an adjacent crossing loop next to the level crossing.
The only odd exception to this is Balhannah Loop in SA where there is a level
crossing in the middle of the crossing loop.How this is worked I cant even
guess.
A track cct is as you have summised, an insulated section of track where
the axles form a short across the tracks to actuate the cct, usually DC but in
electrified areas AC , as the traction current cant be isolated .Im not aware
in Australia of any other methods other track circuiting to actuate level
crossings, other readers may know more.
MD