Safe Speed Forums

Firstly, apologies for the thread title. I have no idea what these things are called.

In the last few years I've noticed a growth in these. At stupid junctions like X and Y junctions they put a metal surround over the green light with angled metal slats obscuring it. The idea is that only the cars that the light is meant for get to see the green light and thus people from the other part of the junction don't go at the same time. ie.(not to scale)

In theory, Car 1 can see the light and Car 2 cannot, therefore Car 2 will not proceed when they aren't supposed to. In practice, I have found that even if you are in the correct lane for a particular light, you can't see the green until you reach the stopline. Even then you have to crane your neck sometimes.

So far, not a major safety issue, until yesterday when, upon approaching a junction that I know well, and is not fitted with these things, the red bulb had gone and I found myself looking at the light and then continuing as if it were on green. After a few seconds I realised what I was about to do and slowed down and double checked the light on the other side of the road (which had previously been obscured by a large van.

I wondered why I'd done this, I knew that junction was traffic light controlled and I know to be especially careful when the traffic lights aren't working. It wasn't untill I happened across one of these obscured lights that I realised what had happened.

With these junctions you are prevented from seeing the green light until you reach the stopline, however you can see the red and yellow lights from a distance. Therefore no light visible means go

Is it just me being stupid or is there a real safety issue in that drivers can become conditioned to thinking that no light = green light thanks to these things?

I would hope that people default to "no light, proceed with caution"! This is something that has official status in France where to avoid the stupid state of people being stuck as Red in the middle of the night, the lights go into a flashing amber mode that allows everybody to proceed as if the lights were not there.

The masking of lights as you say can cause problems, but I really don't think that DfT think about failure modes of their equipment properly, or even the cost of running. We now have LED arrays that consume significantly less power than incandescent bulbs, and that have a much longer life with significantly less chance of a total failure of a single light.

But it would cost to much to replace working equipment so they are only used for new installations... what about reducing the Uk's CO2 output?

Lum - we have those slatted lights on some of the main roundabouts here in Swindon, only these ones are horizontal. They are an absolute menace. As you say, you can't actually see the green light until you're practially underneath it, and from the cab of a lorry you can't see them AT ALL. Bloody stupid - another pointless and dangerous attempt by the DfT of slowing people down IMO.

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Science won over religion when they started installing lightning rods on churches.

The ones I've seen are vertical. Horizontal ones sound crazy as they wont serve the purpose of preventing the green light being misinterpreted as a signal to a different lane. I can't see any possible reason for these unless for some reason green lights scare the local birds (but red and amber dont)

What the hell do you do in a lorry? You are going to have to assume that no light means go which is just what you need in a vehicle that can't stop quickly and is liable to do a lot of damage.

You tell me! I'll try and think on later and go out and take some photos of the offending lights.

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Science won over religion when they started installing lightning rods on churches.

I was going to say that, but you've said it for me Sixy. I'm glad someone else has noticed this, I thought it was just me!

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We are all in the gutter, but some of us are looking at the kerb.

There's some horizontal ones around here too, and you can add my vote to the "damned stupid idea" total... The only time they make even the slightest amount of sense - and even then they're still a complete nuisance - is if you've got two sets of independent lights next to one another, where the furthest set of lights is close enough to look as if they could be repeaters for the nearest set, and where the furthest set turns green before the nearest. Traffic at the front of the queue at the closest set of lights may then see the furthest set changing to green, assume they're just repeaters for the lights they originally stopped at, and set off without noticing that their lights are still on red.

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Chris

Horizontal slats are called sunshades - and do what they say on the tin. For the 15 - 18 hours in a day when the sun iseityher set or behind the sign, they serve next to no good purpose. for the remaining time, when the sun is blaring on the face of the bulb, without the slats you'd never be able to tell if the light was on or off. The presence of the sunshades reduces the time of ambiguity from may hours to perhaps an hour at most. They should not stop you seeing if the light is on as you get closer because the *underside* of the shades should reflect and therefore be visible to the motorist looking up. If a driver is sitting higher than the level of the light, he may have problems as he gets closer. For sites where the light is lower than a standard cab, sunshades should not be fitted. In summary, generally I think that sunshades are good - if done well.

Which doesn't explain why the nearest example to me of slatted lights has, all of about 20 yards away, a set of unslatted lights facing in the same direction, using the same design of head units, controlling traffic in the same lanes, and positioned such that they catch the sunlight in exactly the same way. If the slatted lights were being affected by sunshine to the extent that slats were required, then the adjacent lights would also be affected and should, logically, also then be slatted.

OTOH, my earlier suggestion about these slats being used to "hide" an unsynchronised green light from traffic stopped at an adjacent set of lights does explain why this particular set of lights has horizontal slats fitted to just some of the heads (it was this set of lights I had in mind when describing that scenario).

So, they may have been designed originally to be sunshades, but it seems as if they're being used for other purposes as well, with less than stellar results...




Nice theory, in practice they don't work like that, not even in the middle of the night when you'd expect to have the best chance of seeing any reflections. With the ones around here you have to be within a couple of feet of the stop line AND looking upwards at the light head to see whether the green is lit or not.




IF, yes... I've yet to see any which I'd describe as having been "done well".

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Chris

the horizontal slatted ones i've seen are as twister describes.

i can't see any motivation behind them other than to prevent drivers seeing the green light until a few yards before the stop line. i guess the aim is to prevent drivers accelerating from one set of lights straight through the next... although if they were on green who cares.... and as you approach the 2nd set and cant see the orange or red light (no slats) what are you going to assume? either its green or the lights are out.

There are some of these around here, I don't remember if they are horizontal or vertical. But they don't get in the way.

Now on my occasionaly journey into London there are some where the light not only has slats but a huge pretruding tube coming out of the green and amber lights! You can't see these unless you are amost dead on looking down the tube. This set always scares me, I try to look for the light but always asume the lights are out and someone will try coming from the other direction. I really don't need that level of concentration being used on looking down a tube to see a light.
(I suppose "someone will come at me from the other direction" is a good thing to be thinking when driving anywhere in London! )

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Andrew.

someone has to cos the locals certainly dont

again, i have questioned these things before. i dont like them and if you cant see any light, it causes problems. the red could be blown but how do you know that when approaching? they are even worse in bright light as you have to squint to see the thing. at least in low light, there is a chance of seeing a green glow

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Richie

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