Safe Speed Forums

The Times, January 26, 2006

M-Way traffic lights

Traffic lights are to be placed on entry slip roads to stop drivers joining crowded motorways. The Highways Agency said that the M6, M60 and M62 will be targeted first in an attempt to relieve congestion. Other motorway slip roads in the North East, South East and Midlands will get traffic lights this year.

Rant mode...on Who on earth had this moronic idea? Anybody with half a brain knows that motorway slip roads allow drivers to build up speed to safely join the flow of fast moving traffic. It's in the Highway Code!

If traffic lights are introduced then that would mean that not only drivers on the slip road would slow down and stop, but also the traffic on the main carriageway would do the same and that would ultimately cause tailbacks, rear end shunts, injuries, deaths and motorway closures and I hate to say it but, traffic light cameras Rant mode...off

Paul, whoever had this idea, they should be named and shamed and their stupid measures shot to pieces. If this proposal goes ahead, we'll see a dramatic increase in road deaths and regardless of all the spin, lies and statistics, the fault will lie with the Highways Agency for coming up with this ridiculous idea.

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Anyone who tells you that nothing is impossible has never bathed in a saucer of water.

They already exist in places. In theory, the lights are far enough back to allow acceleration up to motorway speeds before joining, but doesn't happen in practice.
The other main side effect is the build up of traffic on the roads behind the lights, especially at rush hour, blocking up already busy junctions and A roads. M6 J10 spring to mind...

As far as I know, they don't stop the m-way traffic, CJG. They stop the traffic up the slip roads before they get down the ramps. That way, they bottle-up the congestion on the local system, and let the m-way roll on. It's a simple network management trick that has been used on parts of the m-ways for years. It is used to localise congestion. That's all.

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An experiment with, so called, ramp metering was done on the M27 J3 to J7. It was terminated and I have yet to see a report on the outcome. This probably means that it was judged a failure so no embarrassing report was produced. If it had been judged a success then, no doubt, it would have been trumpeted loudly.

I didn't like it at all. At J5 the westbound slip is distinctly uphill from the sliproad lights and is followed by the junction with the M3 which requires serious amounts of merging. OK in my 450bhp car but not much fun for a lorry.

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Malcolm W.
The views expressed in this post are personal opinions and do not represent the views of Safespeed.

see on line at http://www.timesonline.co.uk/article/0, ... 74,00.html

I know that there is one on the M6 just east of Brum city centre, never been down it but always looks strange whenever i see all the cars waiting for the lights.

Junction 5 slip road , not sure how close to the Mway, but it loks too close for comfort IMHO

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lets bring sanity back to speed limits.
Drivers are like donkeys -they respond best to a carrot, not a stick .Road safety experts are like Asses - best kept covered up ,or sat on

They have "traffic dosing" lights on some slip roads in the Netherlands, and while I'm not sure if they're actually "successful", they are definitely not dangerous. This is because:
1. As already pointed out, they are positioned some distance back from the motorway itself, and
2. They only ever seem to be active when the motorway is either crawling at walking speed, or at a complete standstill!

They work by rapidly changing from red to green, allowing only one vehicle to enter the motorway at a time. The road signs also VERY CLEARLY state this too, words to the effect of "only one vehicle to pass when the lights go green".

I have no strong opinion about them either way, as I've said, they're only working when the whole road network is pretty choc-a-block anyway. Perhaps they help a teeny weeny bit. Nothing dramatic as far as I can see though.

What is better - local congestion or a blocked m-way?

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That's a bit like asking if one would prefer to be shot or stabbed to death.

To me, that just sounds like another way to spend our taxpayer money.
If, and only if, they give a marginal benefit, I wonder how much money will be spent to:
-install the lights
-maintan the lights
-get the police there when the light eventually brake
-repair lights due to accidents
-justify their existence in the papers
-pay the hefty bonus to whoever came up with this ridiculus idea
Conicidentally, murder and robbery was on an whole time rise this past year.
Excellent job, well done to the Police and the Government for looking after our interests in an honest way.

Signed: The Mob

more opportunities for scameras - enforcing the red lights

Yes. When I read it back, I see what you mean! But let me put it in different way. Is it more important to keep the backbone of the network running, to the detriment of local traffic, or is it more important to free local traffic regardless of the effect on the backbone?

Hint: If the backbone stops, doesn’t that screw up the local system anyway?

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I have seen the ones on the M27 working once when the road was congested. They were changing very fast, almost like disco lights!
They are at the start of the slip road so there's plenty of road to get up speed, not that you needed it due to congestion.

I thought it was an "interesting" idea and it gave me something to look at while waiting. Ooo pretty flashing lights.

(Ok so they weren't that fast, but there was very little delay in changing)

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Andrew.

That's how congestion control alrgorithms work. When congestion starts, the signals slow the rate of joining traffic. When the congestion ceases, the signals stop slowing the rate of traffic. The idea is to maximise the bandwidth of the backbone, in order to take the strain off the local networks. The theory is that if the throughput of the backbone is not maximised, the local networks suffer even more, overall.

I don't know if it works, or not. It does in some networks. It is possible to implement advanced congestion control alrgorithms, which are large scale models of the system, and involve routing algorithms as well. I would not be surprised if these became a reality in the medium-term.

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I know a slip road in the Leuven area in Belgium with this system.
It is indeed one of the more stupid ideas: it does not work. People are not dumb. When you are not allowed to enter the motorway at that specific entry you go for another one, preferably downstream, so the traffic flow is changing but the motorway gets clogged as before.

Yes. Any functional congestion control system would be global to that stretch of the network. In a partial implementation, a blockage on one node floods queuing traffic to other nearby nodes, having little overall benefit. I've seen something related to this in practice on quite large systems. So piecemeal efforts would definitely suffer the effects you describe. The idea must be to do the whole sub-network, or none at all.

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Would it not be more effective to have information signage before the point of no return to warn about motorway problems. Too often motorway problems seem to be "top secret" , whereas many of the short hops eg M6 10 TO J7 can be made off the motorway , sometimes quicker than on it.

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lets bring sanity back to speed limits.
Drivers are like donkeys -they respond best to a carrot, not a stick .Road safety experts are like Asses - best kept covered up ,or sat on

They use traffic lights on the motorways in america and having driven on them they are excellent.

Basically allows 1 car at a time to enter the motorway at speed, this stops the normal idiot up your a$$ and also prevents any problems with the grey haired brigade getting to the end of the ramp at 30mph with you stuck behind them.

That’s certainly worth considering. I suspect the trouble might be that the signage
would be perceived of as being wrong, even when it is right, due to the fickle nature
of drivers. This is due to ‘game thoery’, and it is a challenge for me to explain.

To maximise the bandwidth of the m-way, the trade-off is to put as many cars on it as
you can, while keeping them travelling as fast as they can yet keeping a decent gap
between them. If the pace slows up due to congestion (too many cars), the bandwidth
is reduced. If the bandwidth is reduced, the pace slows up more, so the bandwidth is
reduced more. Eventually, congestion seizes up the m-way.

Congestion control algorithms pre-empt the condition by limiting incoming traffic
before the limit is reached. They would be less effective if they were not
proactive – they would have to wait until traffic is jammed before kicking in, which
takes away the edge, somewhat!

Now consider an ‘informational’ system as you suggest, rather than compulsion. The
congestion control algorithm would detect the signature of a jam, and send out
information before the jam is a reality. But some drivers would ignore that and join
the system, and not get involved with a jam (which is what the system is meant to do).

This would lead the drivers to conclude that the information was totally guff to start
with. Even though the system was doing it’s job perfectly! An engineer’s life is never
fair.

If enough drivers conclude this, the information system becomes self-defeating,
because then a jam would then happen anyway (!) leading other drivers to conclude
that a jam will happen randomly whatever the signs say! In other words, informational
systems can lead to interesting (but hard to predict) outcomes based on game theory
http://en.wikipedia.org/wiki/Game_Theory.

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