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Traffic lights

Community Veteran
Posts: 7,154
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Registered: 30-08-2007

Traffic lights

Around in this corner of SE England some motorway junctions have recently been sprouting traffic lights on the main carriageway end of their on-slip roads, I've seen them on the M1, M3, M4 and M11, I venture to suggest most are outside but facing towards the general direction of the M25 ring. I would guess that maybe other areas of the country have been getting them as well?
Anybody know how they're supposed to work? or indeed if they're already working, but only at peak times and I just haven't seen them working?
Experience; is something you gain, just after you needed it most.

When faced with two choices, simply toss a coin. It works not because it settles the question for you. But because in that brief moment while the coin is in the air. You suddenly know what you are hoping for.
66 REPLIES
pierre_pierre
Grafter
Posts: 19,757
Registered: 30-07-2007

Re: Traffic lights

Saw a lot of them last summer and a long way from the M25, I assume its to stop those  people who ram there way onto the main motorway and straight into the outer overtaking lane, going down to Cornwall soon via the M25/M4/M5 will have to look.
Another thing that is not quite Highway code was speed limit signs on the entry slip road - 70.  And yes I know that the White Circle with diagonal black - National Speed limit does not mean motorway speed, But that was a new one to me
Community Veteran
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Registered: 30-08-2007

Re: Traffic lights

I take your point pierre, but these traffic lights do not indicate to traffic on the main motorway carriageway (they're not facing on to the oncoming main traffic) only the on-slip road. Does this mean there will in time be some method of stopping traffic on the main road so that traffic stopped on the slip road can get on to it? all sounds very dangerous to me.
Maybe (speculation) overhead gantries will be needed to stop main carriageway traffic, but if it doesn't have actual barriers I can see them not being taken any notice of...
Experience; is something you gain, just after you needed it most.

When faced with two choices, simply toss a coin. It works not because it settles the question for you. But because in that brief moment while the coin is in the air. You suddenly know what you are hoping for.
Community Veteran
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Registered: 30-07-2007

Re: Traffic lights

Quote
Anybody know how they're supposed to work? or indeed if they're already working, but only at peak times and I just haven't seen them working?

We have a few in the manchester area on the M60 ring. They tend be be at junctions with lots of peak time traffic joining the motorway. They only operate when the motorway is busy. All they seem to do is operate on a timed red/green. Thus they reduce the average amount of traffic joining an already busy motorway.
Well , thats the theory I guess. Doesn't work too well in practice cos all that happens is that the traffic enters in large short bursts...
 
itsme
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Re: Traffic lights

Have seen them when on the M6 but have not  actually been on the slip roads. Have been on them in the USA well over 10 years ago and I thought that they worked well. In the USA they work on a one car principle where you are stopped high up on the slip road and a car is released every few seconds, probably every 2-5 seconds. So the affect is that only one car is joining the motorway at a time and the flow is maintained.
The ones that I have seen on the M6 I would say don't work very well as twin lane of cars are stopped low down on the slip road and relased together for 5-10 seconds, so about 10 cars are joining the motorway at the same time.
When I did encounter them in the USA I thought that the system was worth trying in the UK together with turn on right at traffic lights, in the UK it will be turn on left. This is when a car can turn right when the lights are red if the road is clear. Took me a few hours of driving in the USA to work this out, could not understand way other drivers were beeping me when at traffic lights at red. Then saw signs with No Turn on Red and at other lights drivers turning right when the lights were at red.
Community Veteran
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Registered: 12-08-2007

Re: Traffic lights

I think they are to control traffic entering the motorway at busy times.
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Re: Traffic lights

We've had them on the M1 in South Yorkshire for a while now and I too have been puzzled by them - couldn't fathom out what they were for.
Doesn't seem to make a scrap of difference to the traffic on the slip road or on the main motorway.  Huh
VileReynard
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Re: Traffic lights

Many sliproads connect a roundabout to the motorway - so if you block the slip road, you can quickly get gridlock.
Probably a plan introduced by some control freak.

itsme
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Re: Traffic lights

If the motorway get gridlocked then the slip roads will also. Which is what the traffic lights is trying to stop.
The system works well in the USA but I question how it has been implemented in the UK. As I stated above in the USA they release near the top of the slip road one car at a time so they are spaced out by about 50m. By the time they reach the motorway they are going at a similar speed with room to merge in. In the UK they release several cars near the bottom of the slip road so they reach the motorway at a slower speed with several cars trying to merge in the same gap.
Community Veteran
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Registered: 31-08-2007

Re: Traffic lights

Well I've seen some appearing near us, not working yet. But it seems damned dangerous to me, unless they are only going to be used when traffic on the motorway is standing a short distance from the junction.
If you are at a stop on the slip round, by the time your reach the motorway only a short distance down, you are going much slower than the traffic on the motorway and filtering will become more life threatening  Crazy Any lights should be on the entrance to the slip road or they should include lights on the main carriageway as well, but then we'd need a lower speed limit on the motorway ....................
Community Veteran
Posts: 7,154
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Registered: 30-08-2007

Re: Traffic lights

I suppose I should have tried this earlier but, if you google "motorway traffic lights" there are any number of links, this dates back to when A Darling was transport minister!! The term used for it is "ramp monitoring"
Experience; is something you gain, just after you needed it most.

When faced with two choices, simply toss a coin. It works not because it settles the question for you. But because in that brief moment while the coin is in the air. You suddenly know what you are hoping for.
Community Veteran
Posts: 18,552
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Registered: 12-08-2007

Re: Traffic lights

Now we know Smiley  Isn't Google a wonderful thing.  Wink
I'm in the US at present and they've hit the headlines over here because of the incident where their google street van was thrown out of an English village where the residents objected to their  houses being being photographed.
Community Veteran
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Registered: 05-04-2007

Re: Traffic lights

I remember seeing the same kind of thing when I visited New Zealand.
The lights would go Green for a few seconds, the back to red and then green again.
Seemed to be controlling the amount of traffic on the slip road at any one time.
I presume they'll only be used if the motorway is busy.
VileReynard
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Re: Traffic lights

What is the optimal speed for maximum load carrying capacity on a motorway?
Too fast and you get large wasteful gaps between cars,
Too slow and you get M25 syndrome.  Smiley
Shouldn't the traffic be controlled by rigourously enforced speed limits on the motorway itself Cry

Community Veteran
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Registered: 12-08-2007

Re: Traffic lights

Parts of the M25 are controlled with variable speed limits around Heathrow.