Lewknor Interchange is junction 6 of the M40. It is immediately to the north of the Chiltern Escarpment, which forces the London-facing slips to be longer than normal in order to reduce gradients.
The junction is used by Oxford-London coaches, turning off, stopping, then rejoining the motorway. The B4009 to the south is lined with car parking spaces to serve this Park and Ride.
Original plan for the junction
Original plans for the M40 show a different layout to what was built. The B4009 bypass of Lewknor was to run slightly to the south of its current route and the London facing slip roads were to be loops which faced the B4009 to the north. The M40 itself is shown as D2M with a crawler lane in the London direction starting at the exit slip.
A proposal for a service area at the junction existed in the mid-1990s.