wrote:

"John Rowland" wrote:
Tom Anderson wrote:

Science:

http://arstechnica.com/news.ars/post...riving-causes-...

I look forward to reading the paper, and to following development of
these ideas in the future.

Obviously if every side road off your commute between your home and your
office was closed, this would speed up your journey. Unless you're Kim
Jong-il, I don't see that as useful info.

But that's not what's being claimed. What is being claimed is that by
closing certain links, journey time for everybody can be improved.

Indeed. It looks like good, well-informed and useful research.

Certain road schemes in the UK have actually been built with the same sort of
consideration in mind - and that's going back over four decades. The
best-known example may well be the M6/A452 junction at Castle Bromwich (then
in Warwickshire), opened to traffic in 1971. The junction:

http://maps.google.co.uk/?ie=UTF8&ll=52.509339,-1.792595&spn=0.009899,0.019312&z=16

.... has slip roads which face only to the east, a move designed to prevent
commuting along the M6 from Castle Bromwich to the A38(M) at Gravelly Hill
and thence to Birmingham City Centre.

This isn't particularly new.

Precisely. But there is always room for proper theoretical and empirical
research in order to test what is often thought of as "common sense".

Perhaps, eventually, some of those junctions along the northern edge of the
M25 (J26 A121, anyone?) will be shut (except for emergency access and egress)
in order to prevent traffic being slowed by rush-hour joiners. I'm fairly
sure that the M25 was never meant to facilitate access to Waltham Abbey in
any event.

However, I'm not sure anybody has
actually tried to predict which roads should be closed to improve
congestion. The wiki page: http://en.wikipedia.org/wiki/Braess%27_paradox
gives a couple of examples where a new road increased congestion and
closing it relieved the congestion again. It also gives the example of
the closing of 42nd street in NYC reducing congestion - however I
don't know if that was luck or planning.

Note that this is different from the claim that new roads cause extra
traffic. This is the case when, everything else staying equal, opening
a new, fast, road can cause all the existing people to see increased
journey times without adding any new journeys.

Again, this is an obvious point. Those who claim that you can't build your
way out of congestion should stop for a moment and ask themselves what would
happen in London if the M25 (including the Dartford Crossing) was closed to
traffic.

And then they should ask themselves whether bilding/re-opening the M25 (they
amount to the same thing) would relieve congestion or not.