A40, A40(M) or M40

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Sort of there and sort of not; sort of built as it was planned in the Ringway era and sort of not. The A40 is probably the most-improved route into London, with work starting on a dual carriageway back in the 1920s and with a mostly grade-separated road now penetrating the urban area right up to the present Inner Ring Road.

The outer, rural section is M40 and was terminated near Uxbridge in the 1970s; the suburban stretch is plain A40 and has been improved piecemeal from the 1920s Western Avenue, and the innermost section was opened in the late 1960s as the notorious A40(M) Westway, a motorway extending Western Avenue right in to Marylebone. How the route might have been upgraded or made more consistent in the Ringway plans is not very clear at this stage.

Continues to High Wycombe & Oxford
R4 Western Section (or at next junction)
Denham Spur & Uxbridge
Local connections to Ickenham & Hillingdon
R3 Western Section
Local connections to Northolt & Ealing
R2 Western Section & R2 North Circular Road (Hanger Lane)
Link to R1 North Cross Route (Gypsy Corner)
Local connections to Shepherds Bush & Acton
R1 West Cross Route
A5 Edgware Road (Marylebone Flyover)
Continues as A501 Marylebone Road

The route

The M40 that we know and (occasionally) love was planned to head for London much as it does today. The line of the Ringway 4 Western Section is not known in this area, but it may have connected to the M40 near the present M40/M25 interchange or further east at present-day junction 1. Certainly preliminary plans can be found showing Ringway 4 coming north past Heathrow to connect to junction 1, and the fact that the M40's planners did not leave a junction number spare for a separate Ringway 4 interchange would hint that this was the preferred option. However, no final choice has yet been found and there are plans in existence showing both possibilities.

At junction 1, as well as the present local connections and the possibility of Ringway 4 joining here, there would also be a short motorway called the Denham Spur striking north-east to connect to Ringway 3 near Ruislip Common. This would seem to explain why the roundabout at M40 junction 1 is so incredibly large. The junction's west-facing sliproads are also designed to accommodate free-flowing links to the Denham Spur (an estimated layout is shown right; click to enlarge), and a source who worked at Buckinghamshire County Council in the 1970s suggests that this provision for the Spur was included in a rather covert manner as the proposals for the Denham Spur and for Ringway 3 were not then very advanced.

Eastward from here, there is little evidence for the Ministry or the GLC's plans, but it seems clear that the existing A40 Western Avenue was supposed to be upgraded to a free-flowing route of some sort to reach Ringway 1. Whether it would have retained the A40 designation, or been M40 or A40(M), is not at all clear. The route today has several large grade-separated junctions which appear to be remnants of a large upgrade programme that was never completed.

The route would meet Ringway 3 itself at either a new junction south-west of Northolt airfield, or at the existing A4180 interchange, depending on whether the Ministry of Transport or the GLC route for Ringway 3 was selected. It would then continue inward, with various local connections on the way, to meet Ringway 2 at the existing Hanger Lane junction where the A40 meets the A406 North Circular. How this might have been upgraded is, again, not clear at this stage.

At Gypsy Corner, another north-east facing motorway spur (shown left; click to enlarge) would have followed the North London Line railway towards the North Cross Route. The existing A40 would have remained the mainline through this junction, though a very substantial portion of its traffic was expected to leave there for the North Cross Route. The rest of the A40 towards central London would have been of secondary importance.

The former A40(M) Westway at Wood Lane. Click to enlarge

A short distance later, the uncertainty ends and the motorway starts again with the A40(M) Westway, a section of elevated motorway built during the Ringway era. This route was one of the few sections of the Ringway plan to get built, opening in 1970. It begins at the A219 Wood Lane, interchanges with the West Cross Route and carries traffic alongside the Hammersmith and City Line railway to end at the Marylebone Flyover on the A5.

From all of this, we get precisely no further in working out what the road would have been called. Again, the junction numbering on the existing M40 offers a clue, having been applied in the Ringway era. With junction 1 at Uxbridge it suggests that the M40 was not destined to get any further in towards London, so a best guess says the road would have reverted to A40 for some distance before becoming a motorway again as the A40(M) closer to central London.

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