Earl Purple wrote:

It is a primary route. I don't know if it always has been though,
before they declassified the part of the West Cross Route that used to
be the M41.

Indeed (though the A-Z doesn't distinguish primary routes from ordinary
A-roads). I wonder if any other primary routes (other than tunnels or
bridges) are closed at night?

Now if only they'd build a "proper" West Cross Route (as I have
proposed and similar to what was originally planned) they would divert
major traffic away from Kensington and Chelsea and onto a
grade-separated non-residential route towards Hammersmith instead
(bypassing Fulham and Putney to meet the A3 near Tibbetts).

That would be very useful, particularly if combined with a
grade-separated Victoria Embankment/Cheyne Walk (!)