From Roader's Digest: The SABRE Wiki
"Better than the South Circular" is all the good most people can find to say about the poor old A406, but given the handicaps it labours under, I think we could do a lot worse than the North Circular Road... which isn't to say it doesn't need improvement desperately in some spots, but we'll address those in order.
Section 1: Gunnersbury - Brent Cross
In fact the westernmost stretch is the first example of a part that's wholly inadequate for its task, from the A4/A406/A205/A315 roundabout near Gunnersbury station where it begins north to the even more notorious Hanger Lane Gyratory System being traffic-clogged misery at almost any hour of the day or night. (Take my tip if you're heading for the M4 or M3 from the A406 northwards, come off on the A40 and sneak down the Hayes by-pass A312 instead). Never were speed cameras installed to less purpose than the ones on this single-carriageway section to Gunnersbury Park, which crawls over traffic lights at the junction with the A4000/B4491 and another set with the A4020 Uxbridge Road junction. Past this comes a third bottleneck, a railway bridge that looks as though it was constructed from Meccano, which forces all traffic to slow down for fear of becoming airborne as though coming off a ski jump. It is to weep. And we aren't even at Hanger Lane yet...
Ah, here we are at the Hanger Lane Gyratory. Crawl onto the roundabout, thread your way round, avoid traffic veering between lanes, don't be fooled by the exit for the A4005 which appears to be the carry-straight-on option, and NOW, hard left onto the A406, GO GO GO. Phew. Made it. When this junction is free-flowing, that's the way to approach it. When it's clogged, you at least get time to consider your options at leisure...
And now at last we come to a decent stretch of three-lane highway, speeding off past grimy industrial units and furniture hypermarkets, under a mass of railway lines at Stonebridge Park and onwards into the grimy reaches of north west London as three lanes drop to two. There's a grade-separated junction with the A404, and then more damn traffic lights by a MacDonald's just short of Ikea and Tesco. Pressing on we come to another Meccano-bridge, though this one is of a decent size and flatness, over more railway. Over another graded junction with the A4088 and we now have houses and grimy little shops alternating with small factory units on either side of the road—not a very welcoming sight for the visitor to London, especially since a good number of them are derelict.
Section 2: Brent Cross - Bounds Green
Soon a flyover heaves into sight ahead and signals the presence of Brent Cross. Up we go, crossing first the A5 and then the Staples Corner roundabout with the M1 well below us. (Is Staples office superstore named after the junction, or vice versa? Small no-prize for anyone who can tell me). Traffic from the M1 and A5 merges in a jumble of lanes, and as vehicles from the A406 heading for the A41 are also crossing lanes here, care and a steady eye on mirrors are de rigueur. We pass under the A41 roundabout (a very compact three-level stacked roundabout), slow down to avoid the speed camera just beyond (not obvious at all until it's too late) and now we have houses to the side of the road once more.
Traffic lights bring things to a standstill anyway just past this camera where we cross the A502 (no right turn for Golders Green...) and even once you're through them traffic tends to crawl as we're now approaching the A1 junction, with more lights. This stretch is another one that was in need of improvement; the A406 and A1 multiplex for several hundred yards through Henlys Corner, including a further set of lights with the cheeky little A598 demanding a fair crack of the whip. In 2011 Transport for London improved the junction by creating a half hamburger arrangement with displaced right turns from the A406 to the A598 and widening of the main line of the A406 from 3 to 4 lanes each way between the two A1 junctions.
The new stretch of road from here was upgraded from another very slow part, with the A504 denied a junction as it crosses overhead, and we dive under a pleasantly-styled brick underpass and over the crest of a hill to a graded junction with the A1000, which is the old A1, near Finchley Lido cinema and restaurant complex. Beware another speed camera on the next stretch as we come up to Colney Hatch (where they used to have the famous loony bin, but now have a Tesco — there's a lesson in that somewhere) and a graded junction with a mere B road, the B550 or the B505 (maps suggest the former, but the road signs at the interchange shamefully refer to either number with no consistency at all! Somebody shoot whoever proofread those signs)
Past another retail park and three lanes drop to two as we sneak through a long bridge, almost a tunnel, under the main railway line to King's Cross. Between this and the set of traffic lights with the A109 just beyond this is another section ripe for improvement, but how to fit any kind of graded junction into the space where the railway cramps things up is a tough one to crack.
Section 3: Bounds Green - Chingford
This is the start of the notorious Bounds Green stretch. The next bit used to be a three-lane-total road with a suicide lane in the middle, and few tears were shed when that was done away with, I'll warrant; it was like a banger racing circuit on a bad day. But, as Shakespeare says, "thus bad begins but worse remains behind" -- next thing we find is a traffic light controlled crossroads with a TOTSO, where to stay on the A406 you need to turn right! Both lights and lane markings are set up to facilitate this movement but it's still a pig and has no place still existing. Of course the plan to upgrade it was nished a few years ago, after the compulsory purchase of houses at the roadsides... The other arms of the crossroads are the anonymous A1110 and B1452.
Having made our right turn we crawl along the next stretch, through more traffic lights with a further B-road junction (B106 for Bounds Green station and Muswell Hill). Little residential roads come off here on either side, some bollarded off, others not as they are dead ends and the A406 is their only access. One, Palmerston Road (no right turn into it going eastbound) actually used to be the B151, and part of it still is according to Streetmap, which I find incredible as it's an entirely ordinary urban residential road clogged with parked cars and serves nowhere that the A406 or A105 don't...
The next interchange is signed as Clockhouse Junction, though no locals call it anything other than 'Palmers Green traffic lights'. For westbound traffic these are the first lights since Barking and too many drivers forget they're not on a motorway and find themselves buried in someone else's boot here. I'm sure it's no coincidence that Claims Direct used to have an office right by the crossroads. But once you're through heading west, the road becomes dual again and at last we're free to put the pedal down for a while, speed cameras notwithstanding.
We can roar underneath the Great Cambridge roundabout with the A10 and A111 giving it hardly a glance, past the North Middlesex Hospital to our right, and down the underpass at Edmonton, the most recently completed improvement on the road and which cleared a painfully slow section. That was the A1010 we just went under (old A10, you know). There's a slightly oddly designed junction next with the nice new A1055 Lea Valley Route to Tottenham Hale which requires 270-degree turns for some manoeuvres, but on we speed, past another big Tesco and a flyover over the A1055 itself. Another strange junction follows with the A1009 for Chingford, where to turn onto it you have to come off, over a roundabout, and make as if to rejoin the A406 before being allowed to fork left and onto the A1009.
Section 4: Chingford - Barking
Another supermarket follows, a Sainsbury's this time, and Walthamstow dog track is also to be found at the next exit, where the roundabout over the road serves the A112 and an uncredited B179. The road then dives deep to pass under the B160 and several residential roads before popping up again at a strange slip road where one can join the A406 eastbound from the unclassified Hale End Road above but where no other entry or exit is possible. This slip road causes conflict between lane-changing traffic for the next set of slips, the Waterworks Corner roundabout with the A104.
I don't know what they surfaced the road with from this roundabout down to the M11, but whatever it is it's about the smoothest drive I've ever had anywhere in the country. Hope they've got some more of it, whatever it is! We pass without an interchange under the old A11 (now A1199), and then the Central Line, as the slip roads begin for the A1400/A113 at Charlie Brown's roundabout and then the M11, which sounds and looks complex, but which in practice seem to work smoothly (makes a nice change for this road). The A1400 was the old A406 before the next stretch south was built in the 1980s, which was meant to be M15 but which was downgraded before even completed...
We're now heading south at a nice steady 50mph (you wouldn't speed, would you?) and there's usually a nice clear run for the last few miles over some graded junctions with roundabouts below; first the A12 by Redbridge tube station, then the A118 (not quite a roundabout below, but a very oddly designed affair involving more 270-degree turns on a tight radius somehow reminiscent of M6 junction 7) and next the A124. Finally the end's in sight; we come up to a big, big roundabout over the A13 where the latter road gets the straight-through route below us and we are decanted onto the roundabout.
Which shall it be, Passworthy? A13 to Docklands and central London? A13, trunk road to the sea, down to Grays, Thurrock and rather near Basildon? The uncharted wilds of the A1020 straight ahead of us, aiming for Beckton and North Woolwich where we can pick up the ferry and take the South Circular round (even more slowly) to where we began? Or shall we just pull into Claps Gate retail park to recover from our exertions in Kentucky Fried Chicken or Pizza Hut? Whatever we choose, our journey on the A406 is over. What's that? Why isn't the A1020 and A117 from this point to the ferry also the A406? Don't ask me, I'm just the navigator...
Section 5: Barking to the River Thames and beyond?
...Because it's not finished yet!
When (if) the Thames Gateway Crossing is ever built the access roads will start at the A13 junction, which will become a three-level stacked roundabout affair, run nearly parallel to the A1020 until it passes Gallions Reach Shopping Park (built on the site of the former Beckton Gas Works, the derelict remains of which were used by Stanley Kubrick to represent war-torn Vietnam) and the large Docklands Light Railway depot. At this point the new road will turn and head south-east towards the river being joined by the already existing slip roads from the A1020 and passing over the unclassified and singled Armada Way. Then comes the fabled Thames Gateway Crossing, originally intended to be a tunnel when Thamesmead on the opposite bank was built, and most recently (January 2012) promised to be a ferry by Boris Johnson (who cancelled the bridge a few years previously). Whatever gets built, if something does, then the A406 moniker will make it to the north bank of the river, but whether it or a zone 2 road will cross the water who knows!
The A406 is described in the 1922 Road Lists as North Circular Road (proposed new road): it did not exist on the ground but bits of it are shown as under construction on the 1923 MoT map of London. Although the road was mostly new build (which opened in stages), certain stretches were renumbered from existing roads, for example the A405 in the west. In 1928 the ridge carrying Wadham Road over the railway line at Hale End opened, replacing a level crossing.
From the 1960s the central section of the North Circular (between the A40 and A11) was upgraded as part of Ringway 2 (although the ringway was cancelled before the upgrades were fully completed); the western and eastern sections, however, were not upgraded as the ringway was proposed to have a different line. Ringway 2 east of the A11 was originally planned as a motorway, the M15, and although the original plans were cancelled part of its route (between the A11 and A13) was built in the 1980s as an extension of the A406; the original section east of the A11 became the A1400.
The original alignment around Waterworks Corner deliberately avoided Epping Forest. It diverted from the current route through the forest to run parallel to Becontree Avenue up to the A503, then turned left to Waterworks Corner, meeting the A104. The old road on the western edge of the forest up to the A503 has been completely removed and is now simply a grass field.