Ardley Interchange, often called Cherwell Valley Interchange, is junction 10 on the M40, linking to the A43.
Originally the junction was a standard dumbell.
As part of the upgrade works on the A43 it was redesigned. The redesign is typically cited as a example par excellence of bad planning, as the two main flows (A43 to and from the M40 south of the junction) conflict, where they didn't before.
A Highways Agency study suggested that accident rates here have tripled in the five years since the junction was redesigned, as opposed to the rest of the A43 upgrade where they were reduced. The accidents are associated with higher vehicle speeds and driver congestion, which they suggest is because the M40 onslips are not on the sides drivers may expect them to be. The scheme, compromising of M40 J10 and the A43 as far as Baynards Green, aimed to deliver a cost/benefit ratio of 3.3. The actual measured value was -0.2.