Great Western Coffee Shop

I travelled down on the c2c line a couple of weeks back :)

Then I noticed a signal aspect that i'd never seen before, on the East side of Barking... Double Green...!

Anyone know what this one means?!

Just interested me thats all, I only thought you could get Double Yellows (Signal after next is at Danger) ???

But then, I wouldn't call myself an expert either :D

Are you sure you were not looking at London underground signals?

They have double green because its the green from a repeater signal, and the green from the main signal.

A London Underground repeater signal has a yellow plate and the letter R before the signal number, which is the same as the signal it repeats.  A repeater is only used where necessary for sighting purposes, maybe the platform signal at Barking is obscured by a bridge for example. 

Some locations have a stop signal and a repeater signal mounted on the same post.  This looks like a four-aspect signal but is actually two separate signals.  There will be two identification plates on the signal post, one in white (for the top two aspects) and one in yellow (for the bottom two aspects).

Thanks for the replies...! ;D

Yes it was London Underground the signal is located (There were atleast 3 I counted but it was dark when I was travelling)

The c2c line runs alongisde the District Line from West Ham - Upminster (Where I saw the signals in question)

Eagle-eyed travellers on FGW services into Paddington will be able to spot the signals 'gwr2006' describes as the District Line tracks bear round to the left shortly after Ealing Broadway station.

Just to confuse the issue there are flashing green aspects on the East Coast Mainline between Peterborough and Grantham.
They were originally set up for the class 91's (225s) to run at 140mph under test conditions.

I think the rulebook now states that flashing greens means run at 'enhanced speed'.

Slightly O/T , but I believe that double green signals were proposed, though not AFAIK ever installed, for high speed lines.
A double green would give permission to proceed at a higher speed than single green, for example single green=125 MPH and double green=140MPH.
In fact, as posted above, flashing green was adopted instead for enhanced speeds.

The main reason was financial, double green aspects would require new signals with 5 lamps, but flashing green used the existing signals with addition of a suitable timer to make the lamp flash.

A double green would be easily achieved with LED signals but they were not in use when the decision was made.