Denham Interchange

Denham Interchange is junction 16 of the M25 and junction 1A of the M40. It is very similar in layout to Winnersh and Croft Interchanges, with variations in size and orientation, except that at Croft one left-turn slip road is on the inside.

The creation of this junction meant the moving of the west-facing slips of Denham Roundabout.

History

The earliest known plans for the junction date from 1964 when it was planned to be much closer to Denham Roundabout. The junction would serve not only the M25 and M40 but also Ringway 3. A lack of success at trying to find plans for the junction means the layout is as yet unknown other than reports and correspondence that describe it as spaghetti.

Layout of the four level stack showing the intended braiding between the two junctions

In 1966 Buckinghamshire County Council made their own plans for the upgrade of the North Orbital Road (M25) which was adopted by the Ministry. The junction would have been a four level stack located in the same place as the 1964 proposal. The close proximity to Denham Roundabout meant the slip roads between the junctions would have been braided. The west facing slips at Denham Roundabout were built to accommodate the four level stack. The four level stack proposal lasted until the Ringways were scrapped in 1973.

Following the cancellation of the Ringways there was no longer a need for the connection to Ringway 3 so alternative alignments for the M25 further west were investigated. The four level stack was rejected as being too big and intrusive so alternative layouts were sought. The M25 and junction eventually opened in 1985 approximately 1km west of the original proposals. Ironically the extra distance between the junctions resulted in the westbound entry slip at Denham Roundabout being shortened to increase the weaving length which the originally intended braiding would have solved.

Routes

Route	To	Notes
M25	(M1, M11), Watford, Stansted Airport, Rickmansworth, Harlow
M25	(M4, M3, M23), Heathrow Airport, Gatwick Airport
M40	Birmingham, Oxford, Beaconsfield
M40	Uxbridge, London