From: Brimstone on


"JNugent" <JN(a)noparticularplacetogo.com> wrote in message
news:cPWdnVLJh9_dmUvWnZ2dnUVZ8j2dnZ2d(a)pipex.net...
> Ret. wrote:
>> Ian Jackson wrote:
>>> In message <Ys2dnWruDNukIUjWnZ2dnUVZ8j-dnZ2d(a)brightview.co.uk>,
>>> Mortimer <me(a)privacy.net> writes
>>>> "ChelseaTractorMan" <mr.c.tractor(a)hotmail.co.uk> wrote in message
>>>> news:spcbt5lnro8c6cbjfkd9nikvvii7eucq8h(a)4ax.com...
>>>>> On Mon, 26 Apr 2010 16:07:35 +0100, JNugent
>>>>> <JN(a)noparticularplacetogo.com> wrote:
>>>>>
>>>>>> There just shouldn't be traffic lights at roundabouts.
>>>>>
>>>>> an admission of failure really! There's a tiny roundabout near
>>>>> Lakeside shopping centre, (Essex) with lights on all the (I think) 5
>>>>> entries, they seem permanently switched off, I suspect because the
>>>>> traffic flows better without them.
>>>>
>>>> There was a lot of disruption last year while the Hopgrove roundabout
>>>> near York (A64 goes from dual-carriageway to single-carriageway and
>>>> meets the northern ring road) was modified. One of the changes was to
>>>> put traffic lights on the roundabout.
>>>>
>>>> Throughput on the roundabout is worse than ever, with long queues on
>>>> the single and dual sections of the A64 and on the ring road, at peak
>>>> times.
>>>>
>>>> For some reason, the traffic lights are 24-hour, rather than peak
>>>> periods only. It is infuriating to have to wait at the roundabout for
>>>> ages until the lights change, when you are the only car around late
>>>> at night!
>>>>
>>>>
>>>> The Milton Interchange roundabout under the A34 near Didcot was
>>>> redesigned and traffic lights were put on it. They have dramatically
>>>> improved the throughput of the roundabout - especially at peak
>>>> periods when traffic used to queue for ages to get out of the Milton
>>>> Park business park onto the roundabout. However the phasing of the
>>>> lights is very poor: traffic coming from Milton Park faces two sets
>>>> of lights, very close together (one to enter the roundabout, one to
>>>> let traffic join from Didcot) and they are phased so when one set of
>>>> lights goes green, the next set turns red about five seconds later.
>>>> Often you get the lead car at the first lights doing a wheelspin
>>>> start to try to get through the second lights before it changes.
>>>
>>> On these large intersections, I hate the way that the phasing of the
>>> lights forces you to 'ratchet' your way around the roundabout, from
>>> traffic light to traffic light. Once you actually get onto the
>>> roundabout, I would have thought that it would be more efficient if
>>> you were allowed proceed through two (or even more) sets of lights.
>>
>> It would make more sense to get rid of the roundabout and just have a
>> traffic light controlled crossroads! They seem to manage perfectly well
>> without roundabouts in the US.
>
> For certain values of "perfectly well"; with a set of traffic lights at
> almost every *single* intersection on the grid-iron of Manhattan, progress
> is painfully slow, whether by vehicle or on foot.
>
> The whole idea of a roundabout is to keep traffic moving without
> unnecessary delays. Using lights on the carriageway of a roundabout is
> absolutely crazy since it prevents the natural function of the gyratory
> system by herding the traffic together which reduces the space necessary
> for the essential lane-changing.
>
> *If* there is a pre-empting flow of traffic from one or more directions
> into the roundabout, that could be balanced by a free-standing set of
> lights controlling the flow into the roundabout from those directions
> only, rather like the "ramp-metering" now used on some motorway
> slip-roads.
>
Surely the most sensible solution for that type of junction is a
flyover/under for the route carrying the majority of the traffic, i.e.
motorway style.


From: JNugent on
Brimstone wrote:
>
>
> "JNugent" <JN(a)noparticularplacetogo.com> wrote in message
> news:cPWdnVLJh9_dmUvWnZ2dnUVZ8j2dnZ2d(a)pipex.net...
>> Ret. wrote:
>>> Ian Jackson wrote:
>>>> In message <Ys2dnWruDNukIUjWnZ2dnUVZ8j-dnZ2d(a)brightview.co.uk>,
>>>> Mortimer <me(a)privacy.net> writes
>>>>> "ChelseaTractorMan" <mr.c.tractor(a)hotmail.co.uk> wrote in message
>>>>> news:spcbt5lnro8c6cbjfkd9nikvvii7eucq8h(a)4ax.com...
>>>>>> On Mon, 26 Apr 2010 16:07:35 +0100, JNugent
>>>>>> <JN(a)noparticularplacetogo.com> wrote:
>>>>>>
>>>>>>> There just shouldn't be traffic lights at roundabouts.
>>>>>>
>>>>>> an admission of failure really! There's a tiny roundabout near
>>>>>> Lakeside shopping centre, (Essex) with lights on all the (I think) 5
>>>>>> entries, they seem permanently switched off, I suspect because the
>>>>>> traffic flows better without them.
>>>>>
>>>>> There was a lot of disruption last year while the Hopgrove roundabout
>>>>> near York (A64 goes from dual-carriageway to single-carriageway and
>>>>> meets the northern ring road) was modified. One of the changes was to
>>>>> put traffic lights on the roundabout.
>>>>>
>>>>> Throughput on the roundabout is worse than ever, with long queues on
>>>>> the single and dual sections of the A64 and on the ring road, at peak
>>>>> times.
>>>>>
>>>>> For some reason, the traffic lights are 24-hour, rather than peak
>>>>> periods only. It is infuriating to have to wait at the roundabout for
>>>>> ages until the lights change, when you are the only car around late
>>>>> at night!
>>>>>
>>>>>
>>>>> The Milton Interchange roundabout under the A34 near Didcot was
>>>>> redesigned and traffic lights were put on it. They have dramatically
>>>>> improved the throughput of the roundabout - especially at peak
>>>>> periods when traffic used to queue for ages to get out of the Milton
>>>>> Park business park onto the roundabout. However the phasing of the
>>>>> lights is very poor: traffic coming from Milton Park faces two sets
>>>>> of lights, very close together (one to enter the roundabout, one to
>>>>> let traffic join from Didcot) and they are phased so when one set of
>>>>> lights goes green, the next set turns red about five seconds later.
>>>>> Often you get the lead car at the first lights doing a wheelspin
>>>>> start to try to get through the second lights before it changes.
>>>>
>>>> On these large intersections, I hate the way that the phasing of the
>>>> lights forces you to 'ratchet' your way around the roundabout, from
>>>> traffic light to traffic light. Once you actually get onto the
>>>> roundabout, I would have thought that it would be more efficient if
>>>> you were allowed proceed through two (or even more) sets of lights.
>>>
>>> It would make more sense to get rid of the roundabout and just have a
>>> traffic light controlled crossroads! They seem to manage perfectly
>>> well without roundabouts in the US.
>>
>> For certain values of "perfectly well"; with a set of traffic lights
>> at almost every *single* intersection on the grid-iron of Manhattan,
>> progress is painfully slow, whether by vehicle or on foot.
>>
>> The whole idea of a roundabout is to keep traffic moving without
>> unnecessary delays. Using lights on the carriageway of a roundabout is
>> absolutely crazy since it prevents the natural function of the
>> gyratory system by herding the traffic together which reduces the
>> space necessary for the essential lane-changing.
>>
>> *If* there is a pre-empting flow of traffic from one or more
>> directions into the roundabout, that could be balanced by a
>> free-standing set of lights controlling the flow into the roundabout
>> from those directions only, rather like the "ramp-metering" now used
>> on some motorway slip-roads.
>>
> Surely the most sensible solution for that type of junction is a
> flyover/under for the route carrying the majority of the traffic, i.e.
> motorway style.

That would mean spending the odd million of the billions collected from
road-users.
From: Mortimer on
"JNugent" <JN(a)noparticularplacetogo.com> wrote in message
news:cPWdnUzJh98amUvWnZ2dnUVZ8j1i4p2d(a)pipex.net...
> Someone else is paying (in longer journey times) for that extra capacity
> from that direction.

Sometimes the very fact of putting lights there slows down all the traffic
and creates queues that didn't exist before, rather than simply shifting the
queue from one direction to another.

In Abingdon, they changed the road layout in the town centre and created
queues that didn't exist before, by creating conflicting movements that need
to be controlled by lights when previously the traffic was all moving in the
same direction and simply merged without needing time-sharing of exclusive
access across junctions.

Previously: http://img691.imageshack.us/img691/2287/then.jpg

Now: http://img9.imageshack.us/img9/4167/nowd.jpg

By changing one of the roads from one-way to two-way, it requires traffic
lights at each end to regulate the conflicting movements that it creates.

The only benefit is to reduce the amount of traffic that uses the right and
bottom parts of the triangle. But this is at the expense of traffic backing
up in all directions at the traffic lights, rather than being able to flow
freely. The bottom section has less traffic, but it is stationary, nose to
tail, when previously there was more traffic but it was flowing.

Who elects the pillocks that come up with these schemes?

From: Clive George on
On 26/04/2010 22:28, Ian Jackson wrote:

> I'm firmly convinced that the people who are responsible for the design
> and implementation of these traffic systems only 'go through the
> motions', and have absolutely no interest in optimising the flow of
> traffic.

The professionals who do this sort of thing for a living would disagree.
There's a lot of modelling going on, and stuff which isn't necessarily
obvious (why ped xings are staggered was one which I learned a few
months ago).

Doesn't stop them cocking it up sometimes, eg the A43/M40 junction where
the crossing streams makes traffic leaving the motorway stop at bust times.

Re comments about ratcheting round them - on the ones I use, I'm on the
popular route, and most often get to go round in one go after joining
the roundabout.
From: Clive George on
On 26/04/2010 22:55, JNugent wrote:

>> Surely the most sensible solution for that type of junction is a
>> flyover/under for the route carrying the majority of the traffic, i.e.
>> motorway style.
>
> That would mean spending the odd million of the billions collected from
> road-users.

See A34/M4 junction.
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