Anil Kumar wrote:
Will someone please explain how this is done?
I'll try, but read this with the understanding that my experience is
with North American railroad systems, which may work a bit differently.
Railway signal systems place low voltages across the rails (often 1.5
volts or less). When this is shunted by the presence of a train (or
other conductor), relays detect this and set signals to display Stop
indications.
I once came upon an auto accident at a grade crossing and used the
jumper cables from my car to short the rails and prevent additional
carnage. As a result of the unexpected red signal, the next train
approached the scene at a walking pace, rather than at speed.
Sections of track are electrically isolated from one another with
insulated joint bars. These are easily identified by the plastic color
and size from conductive, metal joint bars. Normally, bypassing one of
these insulators will only connect two adjacent blocks, and is unlikely
to stop a train.
OTOH, any place there is a switch or crossing, there are rails that
cross from one side to the other and shunt the running rails if not
insulated. If one of these gaps is bridged, then a Stop indication is
likely. I'm a bit surprised to hear that a coin is sufficient, but then
I haven't exactly tested this point.
Questions?
Bruce Metcalf,
Lake Buena Vista, Florida
