On Wed, 15 Feb 2017 10:26:15 +0000
Neil Williams wrote:
On 2017-02-15 09:38:59 +0000, d said:

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.

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

On Wed, 15 Feb 2017 04:41:39 -0600
wrote:
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

On Wed, 15 Feb 2017 10:46:24 -0000
"tim..." wrote:
wrote in message news
On Wed, 15 Feb 2017 00:10:31 +0000
Neil Williams wrote:
On 2017-02-14 23:01:46 +0000, Richard J. said:

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

On 15/02/2017 13:50, d wrote:
On Wed, 15 Feb 2017 10:26:15 +0000
Neil Williams wrote:
On 2017-02-15 09:38:59 +0000, d said:

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.

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:

,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

On 2017-02-15 13:50:41 +0000, d said:

Which is when a normal signalled junction should have been installed.

Which would reduce the capacity of the junction by around 25%.

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
--
Neil Williams
Put my first name before the @ to reply.

In message , at 12:02:15 on Wed, 15 Feb
2017, Basil Jet remarked:
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

On 2017-02-15 15:02:33 +0000, Roland Perry said:

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
--
Neil Williams
Put my first name before the @ to reply.

In article , d () wrote:

On Wed, 15 Feb 2017 04:41:39 -0600
wrote:
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!"

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

On Wed, 15 Feb 2017 14:09:08 +0000
Robin wrote:
I'd like to see you implement that or any other of your designs at the
Redbridge roundabout:


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

wrote in message news

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