Peter Frimberley wrote:

http://www.a40actonbridges.info/index.php


But I too had assumed (when driving through the road works at the site
now) that it was both a replacement and widening project. I thought
that was what they bought all those houses up and demolished the
cinema for a few years ago, so they could widen the whole lot to three
lanes! Seems madness to leave it at only two lanes.

The houses were bought and demolished when grade separated junctions were
planned for Gypsy Corner and Western Circus aka Savoy Circus.