A40/Central London - Denham

Section 1: City of London - Marylebone

The A40 once started at the Bank but with the declassification of most roads in the City of London, it now officially starts on the A1 at the Rotunda, London Wall. Between St Martin's le Grand and Holborn Circus the A40 defines a boundary between zones 3 and 5 – this situation of a road defining a boundary between two zones, neither of which it belongs to, is also to be found on the A8 in Edinburgh. Between Holborn Circus and Marble Arch, the A40 defines the Zone 4/5 boundary.

After Holborn Circus the A40 continues along Holborn, High Holborn, and Oxford Street, to Marble Arch although only the upper classes (in their taxis) and lower classes (in their buses) are allowed to use the Oxford Street section. The middle classes in their own cars take the A5204 (better known as Wigmore Street).

Like the A3/A24 in south London, the straight alignment of this road, all the way from the Bank to Shepherds Bush, made it ideal for building one of the earliest deep- level tube lines in London, the Central line, without sharp bends or risking undermining foundations. However, because the road is quite narrow, the tunnels in places are built above each other, rather than side by side. This is best seen at Chancery Lane station.

Until demotion of the A40(M) to A-road status, the actual A40 continued from Marble Arch along Bayswater Road and Holland Park Avenue to Shepherd’s Bush, (the present A402), and then up Wood Lane past the BBC to join the present route at Western Avenue. Even further back in history, it continued from Shepherds Bush up the Uxbridge Road (the present A4020) through Ealing and Southall to Uxbridge. Now, it disappears at Marble Arch, presumably multiplexing with the A5 on the Edgware Road before somehow reappearing as the Marylebone flyover (which has no direct access from the Edgware Road).

Section 2: Marylebone - Denham

From the Marylebone corner the A40 rises up onto the Westway, a major piece of engineering which was completed circa 1969. It's one of the rare pieces of (ex-)motorway in the UK which travels for a fair distance on stilts, the M6 around Birmingham probably being the only longer section. There is also a maze of roads situated under the Westway here making up part of the A404. On your left travelling west you pass the Metropole hotel and then the Paddington on-slip joins from the left. This road leads from Lancaster Gate and the Bayswater Road (the old A40). This slip, and the equivalent off-slip, cross the GWR by large girder bridges, the on-slip joining the westbound carriageway being accessed through residential streets! The A40 continues, taking a gentle left hand bend where the Hammersmith and City line travels alongside, though on a slightly lower elevation. Travelling eastbound on this stretch, one can see a somewhat unusual (and almost certainly incorrect) sign halfway along the viaduct; an 'End of Red Route Clearway' sign ... on the middle of the Westway!??

On the left are the new BBC buildings which were built upon the old White City athletics and greyhound stadium. The blocks of flats with their dark red bricks were once part of the Olympic village when London had the honour of holding them in 1948.

The Westway ends as a flyover over the A3220 (formerly M41, part of the Motorway Box) and Wood Lane (A219: formerly A40), running into Western Avenue, which was originally to have been called the A403. This section is 3 lanes wide until you reach the next junction, Western Circus, a traffic light controlled junction which is snarled up almost constantly. The road now narrows back down to 2 lanes again. In the mid-seventies, the A40 was infested with roundabouts and traffic lights all the way to the motorway, and now this set, along with Gipsy Corner (A4000; Horn Lane) are all that remains. An abortive road widening project, with flyovers over the Western Circus and Gipsy Lane junctions, was stopped only after all the houses had been demolished -– the road now runs through a swathe twice as wide as it is.

We are climbing slightly on this section and we cross the GWR again at the top of the hill. We then drop again at the other side to more evidence of house clearance at the Gipsy Lane junction. The A40 now returns to its 3-lane status and makes the journey up towards Park Royal. Swinging to the right, we now encounter the Hanger Lane Gyratory system. The A40 definitely has the best of the junction as it passes right underneath. Despite this major flow being taken out of the way, the Gyratory system is still a major congestion headache for any other flow using it.

The Hanger Lane underpass

The Hanger Lane junction was remodelled in the 1980s, supposedly to cope with modern traffic levels, including the construction of the northbound limb of the gyratory system, making the tube station an island. Previously there was a simple crossroads at the junction, with the (1960s?) underpass passing underneath. People say this is a badly designed junction, but as with most old roads it wasn't built with the idea of today's traffic flows using it. The A40 dives under the junction in a 2-lane underpass. Past the Hanger Lane junction we return to 3 lanes and pass the Vanguard building on the right hand side, which on occasion has had a Harrier Jump Jet perched on its roof!!

On the right hand side we pass the marvellous Hoover building. This was to be knocked down until such protest was made that the front became a listed structure. The rear of the building has now been knocked down and replaced with a Tesco superstore! This is an excellent site at night when the green floodlit glow makes the building stand out.

The A40 now enters the visibly improved section up towards the M40. We then pass the B452 (ex B456) junction, where the A40 again dives under the junction. The old T junction can still be seen just before the large pub and petrol station on the left. We then go under one of the suburban railway lines and over the A4127 junction at Greenford. The next junction is the "Target Roundabout" for the A312, the junction is so named because of the pub which stood at the side; it's now a fast food drive-in!

The original route of the A40 carried straight on here and up to a traffic light controlled junction with the A437 at Hillingdon Circus. This is the most recently improved section. The road now swings off to the right and under the A437 and Metropolitan line under a unique double bridge: the road passes under the railway, which is in turn crossed by the A437. Hillingdon underground station was also rebuilt as part of the scheme.

The A40 rejoins its original alignment and starts the small climb to Swakeleys Junction at Uxbridge. We now go back downhill on the viaduct over the Colne Valley and Grand Union Canal, and on towards the M40 junction. This junction, where the old A40 (now the A4020) rejoins, is a "Magic Roundabout" style one, where you are allowed to go round the "wrong" way. The original line of the A40 can still be seen going straight through the middle.

• ⬅ A40 to Wheatley