Re: Crossing loop design (r.e. Southern Aurora crash)

["MattyQ" <matticue@corplink.com.au>]

Reuben Farrelly wrote in message <7a2jie$is1$1@eplet.mira.net.au>...
>>In Victoria this is called three aspect signalling. There are two
>>lights that can show up to seven combinations:-
>>G/R - clear normal speed "Top Green" in driver speak.
>>Y/R - normal speed warning "Top Yellow"
>>R/R - stop "On the red"
>>R/Y - medium speed warning "Bottom Yellow"
>>R/G - clear medium speed "Bottom Green"
>>Y/G - reduce to medium speed "Reduce"
>>G/Y - clear on a repeating signal (a repeater in Vic is like a
>>distant).
>
>This is probably going to seem like a pretty dumb question, but this system
>as outlined above seems very un-intuitive.  Do you guys have to learn this
>off by heart, or is there some logical rule which explains how things work?
>Like, do you see R/Y and just "know" the indication, or can you apply some
>sort of "formulae" to work out what it means?


There is a formula and it is quite simple. The standard Victorian signal has
2 three aspect signal heads on each post (lets not get into low speeds
etc.). Each signal head can display red, yellow or green. The upper signal
head denotes full track speed. The lower signal head denotes medium speed
which, in the Book of Rules, is 40km/h (again, lets not get into 65's etc).

If a proceed aspect (G or Y) is displayed in the upper head only, you may
proceed at full track speed for that area.  If a proceed aspect (G or Y) is
displayed in the lower head only, you may proceed at medium speed. In both
cases, the other signal head will be Red.

The "Reduce to Medium" indication is the only one on a home signal that
displays a proceed indication in both signal heads. The upper head will be
yellow, the lower green. The upper head is basically saying "The nomal speed
aspect in the next signal will be red". The lower head is saying "The medium
speed aspect is at proceed" therefore, you are required to reduce the speed
of your train to 40km/h by the time you reach the next signal. If you were
approaching a turnout, the aspect sequence would be :-

              G                                    Y
R
 ______R________________G___________________G__  _________

\                            G

\____________R ___