On Sun, 19 Oct 2003 17:34:48 GMT, "Martin Underwood"
wrote:


"Robert Woolley" wrote in message
.. .
On Sun, 19 Oct 2003 17:18:43 +0100, Andrew P Smith
wrote:

In article , Robert Woolley
writes

Speed does kill. You don;t have to be a genius to understand that the
faster the speed of a vehicle, the longer it takes to stop. And the
faster it hits something else the greater the damage.

No. Bad driving kills. The driver selects what speed they drive at. If
that speed is inappropriate then it's bad driving. Nothing else.

I'm a former member of the Institute of Advanced Motorists. Are you?

Nope.

But I hold a PSV licence, gained after comprehensive training. I also
hold a RoSPA road safety engineering certficate, a BSc in Transport
Management and Planning, Chartered Membership of the Chartered
Institute of Logistics and Transport, plus Corporate Membership of the
Institution of Highways and Transportation.

OK. Maybe you can answer this question: what are the circumstances under
which a single 4-way roundabout should be replaced by two linked 3-way mini
roundabouts? There's a sod of a junction near me which always gets snarled
up with traffic (junction of Drayton Road, Spring Lane and the two halves of
Ock Street in Abingdon) and it seems to me that it would have a much greater
throughput of traffic if it was converted back to a single larger roundabout
because it would save drivers having to check twice for vehicles from their
right - once on the first roundabout and then again on the second.

Sounds potentially if signals (traffic lights) might be better.

Roundabouts work best when the flows are reasonably balanced (i.e.
main road has the majority e.g. N-S with few right turners N - W).

I have a junction locally to me in Wembley which has the same problem.
LB Brent have tried all sorts of different approaches and stuck with
the double mini-roundabouts.

Usually you replace a 4 way roundabout with double minis if the
movements are relatively self contained within each mini.

Eg.

OLD:
N
W E
S

NEW:

N
W
^
|
E
S

In this situation, it make sense if W/N and S/E flows are heavy,
because you have independent mini roundabouts.

If N/S flows are heavy, then as you say you get the problem of right
turners.

Of course, any situation whe

a) land is constrained
b) flows are heavy (and the junction is over capacity)

won't be resolved by fiddling around. Either you restrain the traffic
(provide chokes to restrict traffic approaching the junction) or you
undertake demolition and land take.


Rob.
--
rob at robertwoolley dot co dot uk