Discussion:
Paris Shows The Way!
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Robin9
2017-02-14 16:30:18 UTC
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British politicians, particularly those in London, love to
pretend that they are concerned about traffic congestion
and the consequential air pollution. They persist with policies
which have been proved not to work, and refuse to listen
to people who drive in traffic day after day and have a
real understanding of the main cause of the problem.

It seems that in Paris someone in authority is less bigoted
than our politicians:

http://tinyurl.com/jxlb4kc

How refreshing! I am deeply envious


--
Robin9
Richard J.
2017-02-14 23:01:46 UTC
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Robin9 <***@londonbanter.co.uk> wrote on 14 Feb 2017 at
16:30 ...
Post by Robin9
British politicians, particularly those in London, love to
pretend that they are concerned about traffic congestion
and the consequential air pollution. They persist with policies
which have been proved not to work, and refuse to listen
to people who drive in traffic day after day and have a
real understanding of the main cause of the problem.
It seems that in Paris someone in authority is less bigoted
http://tinyurl.com/jxlb4kc
How refreshing! I am deeply envious.
Ealing have been doing that for several years, e.g. the traffic lights
at the T-junction outside Acton Town station (opposite the entrance to
the LT Museum Depot) were replaced by a mini-roundabout and a zebra
crossing about 5 years ago.
--
Richard J.
(to email me, swap 'uk' and 'yon' in address)
Neil Williams
2017-02-15 00:10:31 UTC
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Post by Richard J.
Ealing have been doing that for several years, e.g. the traffic lights
at the T-junction outside Acton Town station (opposite the entrance to
the LT Museum Depot) were replaced by a mini-roundabout and a zebra
crossing about 5 years ago.
Luton airport for years had a terrible congestion problem on a Monday
morning. This started happening soon after a set of traffic lights was
installed at the approach roundabout.

"Get rid of them" said us regulars.

"No" said the airport.

And on it went.

Eventually they did get rid of them, and the problem went away.

The problem with traffic lights, of course, is that they block traffic
movement during the "overlap" between two phases - replace with
something else e.g. a roundabout and traffic can move all of the time.
What you replace it with does require some thought as roundabouts don't
cope well with unbalanced flows, but lights on all approaches to a
junction basically waste time. If lights are needed to balance flows,
not having lights on one branch of the roundabout works quite well -
during the "overlap" time, traffic can then flow from that branch.

Neil
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Neil Williams
Put my first name before the @ to reply.
s***@potato.field
2017-02-15 09:38:59 UTC
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On Wed, 15 Feb 2017 00:10:31 +0000
Post by Neil Williams
Post by Richard J.
Ealing have been doing that for several years, e.g. the traffic lights
at the T-junction outside Acton Town station (opposite the entrance to
the LT Museum Depot) were replaced by a mini-roundabout and a zebra
crossing about 5 years ago.
Luton airport for years had a terrible congestion problem on a Monday
morning. This started happening soon after a set of traffic lights was
installed at the approach roundabout.
Putting traffic lights on roundabouts has always struck me as a ridiculous
thing to do. Its as if the traffic planners didn't quite understand the
purpose of a roundabout or how it worked and assumed it was no different
to a 4 way junction. Once you've added the lights the roundabout is now
completely redundant and you'd probably get better traffic flow if you did
replace it with a simple junction.
Post by Neil Williams
What you replace it with does require some thought as roundabouts don't
cope well with unbalanced flows, but lights on all approaches to a
junction basically waste time. If lights are needed to balance flows,
not having lights on one branch of the roundabout works quite well -
during the "overlap" time, traffic can then flow from that branch.
Roundabouts generally work pretty well on their own. Stirling corner on the
A1 has intermittent lights. The only time serious queues build up is when they
switch the damn things on.
--
Spud
Neil Williams
2017-02-15 10:26:15 UTC
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Post by s***@potato.field
Putting traffic lights on roundabouts has always struck me as a ridiculous
thing to do. Its as if the traffic planners didn't quite understand the
purpose of a roundabout or how it worked and assumed it was no different
to a 4 way junction. Once you've added the lights the roundabout is now
completely redundant and you'd probably get better traffic flow if you did
replace it with a simple junction.
Roundabouts work very well where there is a reasonably balanced traffic
flow on all 4 (or more) arms. They fail badly where the traffic is
highly directional, e.g. towards a city centre.

Consider a typical 4 arm roundabout with arms A, B, C and D positioned
at noon, 3, 6 and 9. If at certain times of day you have a very large
flow from arm B (3 o'clock) to arm D (9 o'clock), it is basically
impossible to get out onto the roundabout on arm C (6 o'clock) because
there is a constant traffic flow preventing this. There are a number
of roundabouts in Milton Keynes where this causes peak time queueing,
particularly as the A421 passes through eastbound in the morning peak
and westbound in the evening peak.

The way to prevent this is to place traffic lights on all but one of
the arms, having no lights on an arm that is not a "blocking" flow but
does have reasonable demand. In the example above, putting them on all
but arm C would allow continuous traffic flow, but would regulate arm B
such that those on arm C could get out and queueing is prevented.

This has an advantage over a traditional traffic light junction as
traffic is always flowing - when the lights are on amber or all on red
for the "overlap", C can flow. With a traditional junction there is
dead time, which with certain designs of junction can be as much of 25%
of the time - reducing overall capacity of the junction. With the
roundabout, this doesn't happen.

Neil
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Neil Williams
Put my first name before the @ to reply.
Basil Jet
2017-02-15 12:02:15 UTC
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Post by Neil Williams
Post by s***@potato.field
Putting traffic lights on roundabouts has always struck me as a ridiculous
thing to do. Its as if the traffic planners didn't quite understand the
purpose of a roundabout or how it worked and assumed it was no different
to a 4 way junction. Once you've added the lights the roundabout is now
completely redundant and you'd probably get better traffic flow if you did
replace it with a simple junction.
Roundabouts work very well where there is a reasonably balanced traffic
flow on all 4 (or more) arms. They fail badly where the traffic is
highly directional, e.g. towards a city centre.
Consider a typical 4 arm roundabout with arms A, B, C and D positioned
at noon, 3, 6 and 9. If at certain times of day you have a very large
flow from arm B (3 o'clock) to arm D (9 o'clock), it is basically
impossible to get out onto the roundabout on arm C (6 o'clock) because
there is a constant traffic flow preventing this. There are a number of
roundabouts in Milton Keynes where this causes peak time queueing,
particularly as the A421 passes through eastbound in the morning peak
and westbound in the evening peak.
The way to prevent this is to place traffic lights on all but one of the
arms, having no lights on an arm that is not a "blocking" flow but does
have reasonable demand. In the example above, putting them on all but
arm C would allow continuous traffic flow, but would regulate arm B such
that those on arm C could get out and queueing is prevented.
This has an advantage over a traditional traffic light junction as
traffic is always flowing - when the lights are on amber or all on red
for the "overlap", C can flow. With a traditional junction there is
dead time, which with certain designs of junction can be as much of 25%
of the time - reducing overall capacity of the junction. With the
roundabout, this doesn't happen.
I'm amazed part-time lights at roundabouts are allowed. It seems obvious
to me that every time a blown red bulb faces traffic already on the
roundabout, you will have traffic joining the roundabout seeing a green
light and thinking it has the priority, and the traffic on the
roundabout seeing no light and thinking it has the priority.
Roland Perry
2017-02-15 15:02:33 UTC
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Post by Basil Jet
I'm amazed part-time lights at roundabouts are allowed. It seems
obvious to me that every time a blown red bulb faces traffic already on
the roundabout, you will have traffic joining the roundabout seeing a
green light and thinking it has the priority, and the traffic on the
roundabout seeing no light and thinking it has the priority.
There will usually (always?) be two red lights. And in any event, green
doesn't mean "full steam ahead", rather than "proceed with caution".
--
Roland Perry
Neil Williams
2017-02-15 15:13:12 UTC
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Post by Roland Perry
There will usually (always?) be two red lights. And in any event, green
doesn't mean "full steam ahead", rather than "proceed with caution".
Yes, with road traffic there is, unlike railway signalling, nothing
ever that says it is absolutely safe to proceed. However, I suspect
most drivers don't treat it that way.

LEDs of course reduce the chance of this, and these days it should be
reasonably easily possible to make all the red lights provable and in
the absence of them all working turn them all off.

Neil
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Neil Williams
Put my first name before the @ to reply.
r***@cix.compulink.co.uk
2017-02-15 22:16:39 UTC
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Post by Neil Williams
Post by Roland Perry
There will usually (always?) be two red lights. And in any event,
green doesn't mean "full steam ahead", rather than "proceed with
caution".
Yes, with road traffic there is, unlike railway signalling, nothing
ever that says it is absolutely safe to proceed. However, I suspect
most drivers don't treat it that way.
LEDs of course reduce the chance of this, and these days it should be
reasonably easily possible to make all the red lights provable and in
the absence of them all working turn them all off.
Pre-LED lights have a second (dimmer) filament which shows some light when
the main filament has failed.
--
Colin Rosenstiel
s***@potato.field
2017-02-15 13:50:41 UTC
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On Wed, 15 Feb 2017 10:26:15 +0000
Post by Neil Williams
Post by s***@potato.field
Putting traffic lights on roundabouts has always struck me as a ridiculous
thing to do. Its as if the traffic planners didn't quite understand the
purpose of a roundabout or how it worked and assumed it was no different
to a 4 way junction. Once you've added the lights the roundabout is now
completely redundant and you'd probably get better traffic flow if you did
replace it with a simple junction.
Roundabouts work very well where there is a reasonably balanced traffic
flow on all 4 (or more) arms. They fail badly where the traffic is
highly directional, e.g. towards a city centre.
Which is when a normal signalled junction should have been installed.
Post by Neil Williams
The way to prevent this is to place traffic lights on all but one of
the arms, having no lights on an arm that is not a "blocking" flow but
does have reasonable demand. In the example above, putting them on all
but arm C would allow continuous traffic flow, but would regulate arm B
such that those on arm C could get out and queueing is prevented.
This has an advantage over a traditional traffic light junction as
traffic is always flowing - when the lights are on amber or all on red
Or just have junctions with the american system of turn on red and at less
busy times simply have flashing orange on all approaches.
--
Spud
Robin
2017-02-15 14:09:08 UTC
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Post by s***@potato.field
On Wed, 15 Feb 2017 10:26:15 +0000
Post by Neil Williams
Post by s***@potato.field
Putting traffic lights on roundabouts has always struck me as a ridiculous
thing to do. Its as if the traffic planners didn't quite understand the
purpose of a roundabout or how it worked and assumed it was no different
to a 4 way junction. Once you've added the lights the roundabout is now
completely redundant and you'd probably get better traffic flow if you did
replace it with a simple junction.
Roundabouts work very well where there is a reasonably balanced traffic
flow on all 4 (or more) arms. They fail badly where the traffic is
highly directional, e.g. towards a city centre.
Which is when a normal signalled junction should have been installed.
Post by Neil Williams
The way to prevent this is to place traffic lights on all but one of
the arms, having no lights on an arm that is not a "blocking" flow but
does have reasonable demand. In the example above, putting them on all
but arm C would allow continuous traffic flow, but would regulate arm B
such that those on arm C could get out and queueing is prevented.
This has an advantage over a traditional traffic light junction as
traffic is always flowing - when the lights are on amber or all on red
Or just have junctions with the american system of turn on red and at less
busy times simply have flashing orange on all approaches.
I'd like to see you implement that or any other of your designs at the
Redbridge roundabout:

<https://www.google.co.uk/maps/search/%22redbridge+roundabout%22+a12+a406/@51.5758967,0.0434959,18z>

(I would put negotiating it when the lights are out of action in the
same class as Sir Thomas Beecham's famous two.)
--
Robin
reply-to address is (intended to be) valid
s***@potato.field
2017-02-15 16:23:12 UTC
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On Wed, 15 Feb 2017 14:09:08 +0000
Post by Robin
I'd like to see you implement that or any other of your designs at the
58967,0.0434959,18z>
(I would put negotiating it when the lights are out of action in the
same class as Sir Thomas Beecham's famous two.)
I've used that junction plenty of times. Tbh I'd say stirling corner and
apex corner are a lot worse but its all subjective.
--
Spud
Neil Williams
2017-02-15 14:58:56 UTC
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Post by s***@potato.field
Which is when a normal signalled junction should have been installed.
Which would reduce the capacity of the junction by around 25%.
Post by s***@potato.field
Or just have junctions with the american system of turn on red and at less
busy times simply have flashing orange on all approaches.
Turn left on red works only where it is safe to have it, and in the UK
we essentially replicate it with flow arrows and traffic islands. And
less busy times aren't the concern, it's capacity reduction and flow
balancing at *busy* times.

I do agree flashing yellow would be better than blank at part-time
lights to avoid wrong-side failures causing accidents.

Neil
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Neil Williams
Put my first name before the @ to reply.
tim...
2017-02-15 16:25:14 UTC
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Post by s***@potato.field
Or just have junctions with the american system of turn on red
which is complete useless at traffic light controlled roundabouts as all of
the traffic is nominally turning left

tim
s***@potato.field
2017-02-16 10:04:03 UTC
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On Wed, 15 Feb 2017 16:25:14 -0000
Post by tim...
Post by s***@potato.field
Or just have junctions with the american system of turn on red
which is complete useless at traffic light controlled roundabouts as all of
the traffic is nominally turning left
Do try and keep up. I was talking about if roundabouts were replaced with
junctions.
--
Spud
r***@cix.compulink.co.uk
2017-02-15 10:41:39 UTC
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Post by s***@potato.field
On Wed, 15 Feb 2017 00:10:31 +0000
Post by Neil Williams
Post by Richard J.
Ealing have been doing that for several years, e.g. the traffic lights
at the T-junction outside Acton Town station (opposite the entrance to
the LT Museum Depot) were replaced by a mini-roundabout and a zebra
crossing about 5 years ago.
Luton airport for years had a terrible congestion problem on a Monday
morning. This started happening soon after a set of traffic lights was
installed at the approach roundabout.
Putting traffic lights on roundabouts has always struck me as a ridiculous
thing to do. Its as if the traffic planners didn't quite understand the
purpose of a roundabout or how it worked and assumed it was no different
to a 4 way junction. Once you've added the lights the roundabout is now
completely redundant and you'd probably get better traffic flow if you did
replace it with a simple junction.
Post by Neil Williams
What you replace it with does require some thought as roundabouts don't
cope well with unbalanced flows, but lights on all approaches to a
junction basically waste time. If lights are needed to balance flows,
not having lights on one branch of the roundabout works quite well -
during the "overlap" time, traffic can then flow from that branch.
Roundabouts generally work pretty well on their own. Stirling corner on
the A1 has intermittent lights. The only time serious queues build up is
when they switch the damn things on.
If you made any attempt to understand traffic engineering, there are
conditions when roundabouts really don't work. If traffic levels are high
and flows unbalanced then some arms can't get out onto the roundabout unless
traffic lights are installed.
--
Colin Rosenstiel
s***@potato.field
2017-02-15 13:55:46 UTC
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On Wed, 15 Feb 2017 04:41:39 -0600
Post by r***@cix.compulink.co.uk
If you made any attempt to understand traffic engineering, there are
conditions when roundabouts really don't work. If traffic levels are high
and flows unbalanced then some arms can't get out onto the roundabout unless
traffic lights are installed.
Translation:
"Just do what I do - read someone elses post then paraphrase and pretend I
knew it all along. Win!"
--
Spud
r***@cix.compulink.co.uk
2017-02-15 15:40:41 UTC
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Post by s***@potato.field
On Wed, 15 Feb 2017 04:41:39 -0600
Post by r***@cix.compulink.co.uk
If you made any attempt to understand traffic engineering, there are
conditions when roundabouts really don't work. If traffic levels are high
and flows unbalanced then some arms can't get out onto the roundabout
unless traffic lights are installed.
"Just do what I do - read someone elses post then paraphrase and
pretend I knew it all along. Win!"
No. I have direct experience acquired over decades of hearing from traffic
engineers. It was pure coincidence that someone, probably with similar
experience, made similar comments which I only saw after posting mine.
--
Colin Rosenstiel
s***@potato.field
2017-02-15 16:31:27 UTC
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On Wed, 15 Feb 2017 09:40:41 -0600
Post by r***@cix.compulink.co.uk
Post by s***@potato.field
On Wed, 15 Feb 2017 04:41:39 -0600
Post by r***@cix.compulink.co.uk
If you made any attempt to understand traffic engineering, there are
conditions when roundabouts really don't work. If traffic levels are high
and flows unbalanced then some arms can't get out onto the roundabout
unless traffic lights are installed.
"Just do what I do - read someone elses post then paraphrase and
pretend I knew it all along. Win!"
No. I have direct experience acquired over decades of hearing from traffic
engineers. It was pure coincidence that someone, probably with similar
experience, made similar comments which I only saw after posting mine.
Sure, complete coincidence. And no doubt you also aquired extensive experience
of air traffic control when you worked for Porcine Airlines.
--
Spud
r***@cix.compulink.co.uk
2017-02-16 01:06:28 UTC
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Post by s***@potato.field
On Wed, 15 Feb 2017 09:40:41 -0600
Post by r***@cix.compulink.co.uk
Post by s***@potato.field
On Wed, 15 Feb 2017 04:41:39 -0600
Post by r***@cix.compulink.co.uk
If you made any attempt to understand traffic engineering, there are
conditions when roundabouts really don't work. If traffic levels are
high and flows unbalanced then some arms can't get out onto the
roundabout unless traffic lights are installed.
"Just do what I do - read someone elses post then paraphrase and
pretend I knew it all along. Win!"
No. I have direct experience acquired over decades of hearing from
traffic engineers. It was pure coincidence that someone, probably with
similar experience, made similar comments which I only saw after posting
mine.
Sure, complete coincidence. And no doubt you also aquired extensive
experience of air traffic control when you worked for Porcine
Airlines.
Do you accept information from anyone or just make silly comments all the
time?
--
Colin Rosenstiel
s***@potato.field
2017-02-16 10:11:59 UTC
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On Wed, 15 Feb 2017 19:06:28 -0600
Post by r***@cix.compulink.co.uk
Post by s***@potato.field
Sure, complete coincidence. And no doubt you also aquired extensive
experience of air traffic control when you worked for Porcine
Airlines.
Do you accept information from anyone or just make silly comments all the
time?
When someone has used virtually identical phrases from someone elses post
made earlier after having not even broached the subject before and then
suddenly claims to have lots of experience in the matter you'll have to excuse
me if I take it with a whole salt mine.
--
Spud
tim...
2017-02-15 10:46:24 UTC
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Post by s***@potato.field
On Wed, 15 Feb 2017 00:10:31 +0000
Post by Neil Williams
Post by Richard J.
Ealing have been doing that for several years, e.g. the traffic lights
at the T-junction outside Acton Town station (opposite the entrance to
the LT Museum Depot) were replaced by a mini-roundabout and a zebra
crossing about 5 years ago.
Luton airport for years had a terrible congestion problem on a Monday
morning. This started happening soon after a set of traffic lights was
installed at the approach roundabout.
Putting traffic lights on roundabouts has always struck me as a ridiculous
thing to do. Its as if the traffic planners didn't quite understand the
purpose of a roundabout or how it worked and assumed it was no different
to a 4 way junction. Once you've added the lights the roundabout is now
completely redundant and you'd probably get better traffic flow if you did
replace it with a simple junction.
bit difficult to do when the roundabout is above a motorway junction

tim
Neil Williams
2017-02-15 10:54:33 UTC
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Post by tim...
bit difficult to do when the roundabout is above a motorway junction
There are plenty of cases where it isn't, e.g. the roundabout in Slough
made famous by "The Office" which was indeed removed and replaced with
a signalled junction.

OTOH, traffic signals on roundabouts often do make sense to solve a
specific problem involving unbalanced flows without reducing the
capacity of the junction.

Neil
--
Neil Williams
Put my first name before the @ to reply.
s***@potato.field
2017-02-15 14:04:46 UTC
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On Wed, 15 Feb 2017 10:46:24 -0000
Post by tim...
Post by s***@potato.field
On Wed, 15 Feb 2017 00:10:31 +0000
Post by Neil Williams
Post by Richard J.
Ealing have been doing that for several years, e.g. the traffic lights
at the T-junction outside Acton Town station (opposite the entrance to
the LT Museum Depot) were replaced by a mini-roundabout and a zebra
crossing about 5 years ago.
Luton airport for years had a terrible congestion problem on a Monday
morning. This started happening soon after a set of traffic lights was
installed at the approach roundabout.
Putting traffic lights on roundabouts has always struck me as a ridiculous
thing to do. Its as if the traffic planners didn't quite understand the
purpose of a roundabout or how it worked and assumed it was no different
to a 4 way junction. Once you've added the lights the roundabout is now
completely redundant and you'd probably get better traffic flow if you did
replace it with a simple junction.
bit difficult to do when the roundabout is above a motorway junction
There will always be exceptions. But having roundabouts as motorway
junctions isn't a requirement. In america the offramp almost always leads
to a junction and in europe its a toss up whether theres one or not though
on the french toll autoroutes there is almost never one at the actual
exit. If there is one its usually way past the toll booths.
--
Spud
tim...
2017-02-15 16:27:27 UTC
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Post by s***@potato.field
On Wed, 15 Feb 2017 10:46:24 -0000
Post by tim...
Post by s***@potato.field
On Wed, 15 Feb 2017 00:10:31 +0000
Post by Neil Williams
Post by Richard J.
Ealing have been doing that for several years, e.g. the traffic lights
at the T-junction outside Acton Town station (opposite the entrance to
the LT Museum Depot) were replaced by a mini-roundabout and a zebra
crossing about 5 years ago.
Luton airport for years had a terrible congestion problem on a Monday
morning. This started happening soon after a set of traffic lights was
installed at the approach roundabout.
Putting traffic lights on roundabouts has always struck me as a ridiculous
thing to do. Its as if the traffic planners didn't quite understand the
purpose of a roundabout or how it worked and assumed it was no different
to a 4 way junction. Once you've added the lights the roundabout is now
completely redundant and you'd probably get better traffic flow if you did
replace it with a simple junction.
bit difficult to do when the roundabout is above a motorway junction
There will always be exceptions. But having roundabouts as motorway
junctions isn't a requirement.
well no

but we do have them

and IME they are invariable the ones where traffic lights have been
installed to "improve" flow

(admittedly not all of them are of the "above the motorway" variety)

tim
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