modern colour lights

In UK practice colour light signals can be two, three or 4 aspect. Generally routes with continuous colour light signalling have three or

Four aspect signals are as you described, but the 4 aspects displayed are red, yellow, double yellow and green. Green indicates that the line is clear, the next signal must be green or double yellow. Double yellow indicates caution the next signal is yellow, Yellow indicates that the next signal is red. Red that the train must stop before passing it. There must be at least braking distance from line speed between double yellow and red signals so signals can be spaced much closer than the 3 aspect case for the same speed.

Two aspect signals are normally used for absolute block sections where the service headways do not justify closely spaced signals. These are installed in pairs in the same fashion as semaphores, red/green 'home' signals are spaced to suit the headway and a yellow/green 'distant' braking distance in rear of each.

The above is just the basics and there are many special cases to do with transitions between one form and another or where local conditions, junctions etc. make it impractical to install the signals at the correct braking distances. Keith

Make friends in the hobby. Visit Garratt photos for the big steam lovers.

I don't know if this is unusual but where I live the semaphore hss been replaced by coloured lights but the signal post - minus arm - still remains complete with accesss ladder and that steel hoop to stop the signalman falling to his death while replacing the lamp. It makes an interesting model subject if nothing else.

(kim)

In message , Piemanlager writes

Simon,

Round these parts (south-east London) there is a new type of 4-aspect signal with just 2 lenses. The bottom lens shows red, yellow and green (but not all at once), and the top one yellow only. The lights behind the lenses are LEDs, and the two lenses are spaced much wider apart than the "ordinary" colour-light signals.

I'm speculating here, having not seen one of these signals, but I wonder if the lenses are on similar centres as the two yellow lenses/aspects in a conventional signal. I suspect if they were mounted closer together distinguishing between a single and double yellow would be difficult at any distance.

Ian

In message , Ian writes

You are probably right.

Correct and the top lenses can also display a red for emergency working.

Also single aspect not to be confused with searchlight signals.

Note that distants are also used with 4 aspect signals where a low density line joins a high density line and therefore have 3 aspects.

A few comments inserted for clarity.

Chris

Modern versions of the searchlight signals, first introduced in the

Chris