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I am interested in canvassing views on this topic as I personally have mixed feelings. Do they ease congestion or are they a major cause? When directions are painted on the road surface and you are the third car in the queue, can you tell whether you are in the correct lane? Drivers who are familiar with such roundabouts seem to deliberately choose the wrong lane at one set of lights to ensure that they are in the correct lane at the next set. Your comments would be interesting.
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Perhaps your mixed feelings are down to their mixed success, I don't think there is a general answer to this.
An example of where they are needed is M1 J21 where the Leicester outer ring road meets the M1/M69. From s/b M1 onto the Leicester ring is a lethal cat and mouse accross traffic sailing at speed out of Leicester and onto the M69. Worse when the Fosse Park shops are busy. There is peak hour control, but not related to shopping hours.
Need is greatest where one inbound route dominates and traffic following it can flow on as though the roundabout was not there. Even then they need to be well planned and precisely timed.
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Traffic lights here look like an admission that the r'about is a failure. The Stafford ring road is (was?) a good example. Almost as good as traffic lights are ped. crossings, sometimes with lights as well. It seems daft to prevent traffic getting OFF the roundabout, but that is what they do !
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If traffic lights are required on a roundabout it is because the roundabout is not of sufficient radius or road width to cope with the volume of traffic, so in that sense they ARE an admission of failure.
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Anyone who knows the roundabout off Jn 9 of the M27 (by TGI Fridays) will probably agree that the traffic lights have made things much better, but you really have to know which lane you should be in (follow the dotted line...) If anyone gets it wrong, it throws the whole roundabout into chaos. If it's running smoothly at rush hour, the lights have reduced the time to get across by half IMHO.
Rebecca
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The RAB of the A34 - M4 has traffic light control and has made progress from the A34 southbound to the M4 Westbound much easier. However this uses the outside lane as a dedicated lane (of 4) and is a much less popular route than either M4 east or straight over the A34 it has much less use than the other lanes. So you can find traffic in it stationary hundreds of yards back from the RAB as people who have either tried nipping down and pushing in aren't able / allowed to squeeze in or people who haven't read the signs try desperately to nudge into the other lanes. Or you get people sprinting off the lights from the outside lane as soon as approaching traffic stops (ie still on red) to cut across traffic and get into the right lane for the next set of lights on the RAB. Or someone creeps forward and sits in the lane and then flips on the left indicator and sits and hopes. Usually they wait until the lights have changed back to Red before they can get across....
They work well as long as everyone understands them and also has consideration for others that don't know / understand which lane to be.
I used to be considered late for work if I turned up later than the boss. On a RAB on the way to work I needed to turn left but there was always a massive queue in the left hand lane waiting to turn left (no lights). I used the Right hand lane and did 450 degrees around the RAB. I would sometimes pass the boss in the queue and have time to make the coffee before he got in....
Piers
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There was a tale going around at my first job about this guy who was often late. He also used to use the lift which was reserved for partners and clients.
One morning he flew through the front door, late as usual, and leapt into the lift to find it already occupied by the senior partner.
"Late again, Jones" said the great man.
"Yes, sir, so am I" replied Jones.
Nothing more was said.
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I travel daily from Ashford to Sittingbourne, joining the M20 at J10 and leaving at J7. J10 has traffic lights, the traffic flow around the RAB is slow at about 10 mph, but it rarely takes me long to get around the required 270°. Joining the RAB is dead easy because I have priority, so the joining queues of traffic clear quickly.
To contrast the J7 roundabout does not have lights. Tightly bunched parades of traffic speed around it at 30-40 mph, so joining to turn right is a nightmare. I have sat for 10 minutes waiting for a queue of 10 cars to clear.
I think I know which I prefer.
Andy
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As Andy says the biggest problem is the speed cars can generate once on the RAB. I have seen a couple of RABs where traffic lights have been installed and they have improved matters.
When wanting to go 270 degrees round a 3/4 lane RAB the difficulty is trying to get from the RH lane to the LH lane.
Bob H
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the first ones i remember were there to let fire engines out of the station, when the most sensible thing to do is turn the lights all to red while the boys are sliding down the pole
that wasnt such a bad idea, many since have been c**p and just bad design
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A large roundabout on the way into Taunton was converted to a traffic light controlled junction (very complex) on a 70mph stretch about 7 years ago. A few weeks after their installation 2 beautiful girls from my college were killed in an horrific accident caused by someone being in the wrong lane at the new junction.
Don't think this ever happened with the roundabout.
Congestion is no different.
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The roundabout over the M40 at High Wycombe is a nightmare. In one place you have to shift two lanes to the left within about 45°. Anyone who isn't familiar with it doesn't stand a chance. High Wycombe commuters can be very unforgiving . . .
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Now if you really want to make up your mind on this, Ray, try turning south from J6 of the M4. It's the Windsor/Legoland road. After about 2m you'll come to a 5-way roundabout with lights. The approach is three lane. Most of the outs are one lane. Just to improve matters, some pointyhead decided to paint crosshatching at the roundabout. However, because its so damn small, you can't help stopping on the crosshatching. Brilliant!
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Same problem at the Army and Navy roundabout at Chelmsford.
Small roundabout with traffic lights and three lanes painted in.
No room for traffic to stack up between the lights.
You need to cut across sharply to get in the correct lane to turn off it.
Not nice.
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