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[email protected] · February 15th 17, 09:41 AM posted to uk.transport.london

In article , d () wrote:

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.

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