JNugent wrote:

The Chiswick section of M4 was designed and built to be
operated at no speed limit whatsoever - though it had the
national 70 limit imposed soon after opening.

You can't design a road for "no speed limit whatsoever". Britain's
motorways were generally designed for 70 mph, but it's obvious that the
first bend on the M4 going west was designed to a lower standard. I
thought the 50 mph limit on that stretch was imposed from first opening,
BICBW.

--
Richard J.
(to e-mail me, swap uk and yon in address)