Two colour traffic lights

[DavidNW9]

I'm surprised there isn't a thread already, rare as they are. There's a pre-Worboys set outside Carisbrooke Castle, but here's a modern one albeit abandoned at Mogden Lane sewage works in Isleworth.

[DavidBrown]

Probably a lot more common than you think - I have to control a set at work (a warehouse/service yard at Tesco) numerous times every day. Most of the time, you will see them off, like in your picture, only being turned on when a vehicle is in the vicinity.

[Chris Bertram]

Surely they're all on private roads. Are there any that aren't?

[DavidNW9]

I'd never noticed them before, but the one at Carisbrooke Castle is on a public road and I think Dover Castle has one outside as well. Glad I've got an example myself though even if new versions. There was a sign on our side (the footpath which crosses the road) which says the lights aren't working so seems permanent.

[Chris Bertram]

I'd never noticed them before, but the one at Carisbrooke Castle is on a public road and I think Dover Castle has one outside as well. Glad I've got an example myself though even if new versions. There was a sign on our side (the footpath which crosses the road) which says the lights aren't working so seems permanent.

Hmm, not convinced that these access roads are actually public roads, even if they are open to the public. Same applies to the toll road from Bryn Glas to Penrhyndeudraeth - it's really a private road open to the public. Good thing that these signals do nothing more complicated that control SALT on quiet roads - like the old 2-colour temporary lights that were superseded during the 60s did.

[traffic-light-man]

There's a pair of Peek Elite Two-colour signals which are for a railway in Trafford Park that crosses a junction. These are ran of the Peek controller controlling the traffic signals, and treats the railway as an arm to the junction.

There also used to be a pair of Mellor heads at our local tip. The same as a pedestrian/tramway crossing signal, they simply had RG lenses in instead of twin ambers.

They're the only ones that I can think of that are actual main-stream manufacturers' signals, as opposed to the likes of Forest City/Signature or Dorman or whatever.

[Vierwielen]

I don't really see the problem, assuming of course that there is a finite time between one green light turning red and the other turning grren.

Of course, given current LED technology, how long will it be before we have single lights which can display red or green, depending on whether a positive or a negative voltage is applied?

[jcpren]

I don't really see the problem, assuming of course that there is a finite time between one green light turning red and the other turning grren.

One role of the amber light is to solve an enforcement problem. With a three aspect signal, if you cross the stop line on red, you are unambiguously guilty of an offence, having had fair warning that it was coming in the form of the amber light. With a two aspect signal, drivers could argue that they didn't have enough time to stop (safely) when the lights suddenly changed from green to red.

Of course, given current LED technology, how long will it be before we have single lights which can display red or green, depending on whether a positive or a negative voltage is applied?

It's already possible, but unlikely to be implemented, as it would lose the most obvious distinction between the lights for colour-blind drivers. ("Signal green" is deliberately bluish to act as a secondary clue.)

[Chris Bertram]

One role of the amber light is to solve an enforcement problem. With a three aspect signal, if you cross the stop line on red, you are unambiguously guilty of an offence, having had fair warning that it was coming in the form of the amber light. With a two aspect signal, drivers could argue that they didn't have enough time to stop (safely) when the lights suddenly changed from green to red.

For this reason, two-colour signals are only suitable for low-speed situations, such as controlling access to car parks.

Of course, given current LED technology, how long will it be before we have single lights which can display red or green, depending on whether a positive or a negative voltage is applied?

It's already possible, but unlikely to be implemented, as it would lose the most obvious distinction between the lights for colour-blind drivers. ("Signal green" is deliberately bluish to act as a secondary clue.)

It's already being implemented across the railway network - however train drivers may not be colour blind, since they already have to view signals in the dark from distance, and cannot easily assess their position in the signal head from afar. Modern LED signals have only one lamp if replacing a two or three-aspect signal, or two if replacing a four-aspect signal, with the second lamp, used for double-yellow only, above the main lamp but spaced so that the two lights remain distinct. But, as John says, this isn't suitable for the road network, where there is no ban on colour blind drivers.

[AndyB]

R/G signals were used at security posts approaching border crossings in NI (sometimes a mile or more from the official land frontier, while the Irish Customs Post could be a matter of yards on the other side, such as on Buncrana Road) to control traffic on approach.

[Chris Bertram]

Modern LED signals have only one lamp if replacing a two or three-aspect signal, or two if replacing a four-aspect signal, with the second lamp, used for double-yellow only, above the main lamp but spaced so that the two lights remain distinct. But, as John says, this isn't suitable for the road network, where there is no ban on colour blind drivers.

Forgot to add that an older form of signal, the 'searchlight', did the same thing using a single lamp with filters moving in front, controlled by voltage. I'd imagine there are none, or very few, left on the rail network now.

[scynthius726]

The TSRGD actually allows for two-aspect signals with a red and amber aspect only. I've never seen one in the UK, but there are plenty in Australia. They are useful for situations where you don't want to give a "full steam ahead" indication, such as where a set of traffic lights is shortly followed by a Give Way. Anyone know if signals such as these actually exist on a public road in the UK?

[Chris Bertram]

The TSRGD actually allows for two-aspect signals with a red and amber aspect only. I've never seen one in the UK, but there are plenty in Australia. They are useful for situations where you don't want to give a "full steam ahead" indication, such as where a set of traffic lights is shortly followed by a Give Way. Anyone know if signals such as these actually exist on a public road in the UK?

Can't think of any, but they're common in Germany, where they are used for ped crossings and to guard rail level crossings.

[worcsfan]

The TSRGD actually allows for two-aspect signals with a red and amber aspect only. I've never seen one in the UK, but there are plenty in Australia. They are useful for situations where you don't want to give a "full steam ahead" indication, such as where a set of traffic lights is shortly followed by a Give Way. Anyone know if signals such as these actually exist on a public road in the UK?

Can't think of any, but they're common in Germany, where they are used for ped crossings and to guard rail level crossings.

Does the B5106 bridge at Llanrwst count?- regulated by level crossing lights at its west end; as its eastern end is flush with the A470 and therefore normal traffic lights would not work.

No green aspect there- you merely go at the western end if the lights are out.

[traffic-light-man]

The TSRGD actually allows for two-aspect signals with a red and amber aspect only. I've never seen one in the UK, but there are plenty in Australia. They are useful for situations where you don't want to give a "full steam ahead" indication, such as where a set of traffic lights is shortly followed by a Give Way. Anyone know if signals such as these actually exist on a public road in the UK?

Do the regulations allow for the cycle R-RA-Blank-A-R though?

[Gareth]

The TSRGD actually allows for two-aspect signals with a red and amber aspect only.

I'm pretty sure TSRGD doesn't allow that. Are you sure you're not being cinfused by with diagrams they have which just shows a red and an amber aspect, with the blank bit below representing where aspects can go in that place than instead of a green ball; these always being arrows?

[nowster]

R/G signals were used at security posts approaching border crossings in NI (sometimes a mile or more from the official land frontier, while the Irish Customs Post could be a matter of yards on the other side, such as on Buncrana Road) to control traffic on approach.

The Irish Customs Post was almost always unmanned when I happened to pass.

[michael769]

The TSRGD actually allows for two-aspect signals with a red and amber aspect only.

I'm pretty sure TSRGD doesn't allow that. Are you sure you're not being cinfused by with diagrams they have which just shows a red and an amber aspect, with the blank bit below representing where aspects can go in that place than instead of a green ball; these always being arrows?

(Pedantry alert!)It allows wig wags which only have two aspects, it also allows red /green two aspect lights at user operated gated level crossings or at toll booths.

(I know neither is what was meant here!)

[Gareth]

^^ As are all pedestrian lights here and in most countries of the world. Even at the traffic lights in the imaginary country that exists in my head...

http://i231.photobucket.com/albums/ee23 ... 1281727041

[irrelevant]

What about these things used in Manchester to indicate stopping at the Rising Bollards? They are off in that shot, but here's another set that's on.