London - Swanley
The A20 starts at the New Cross one-way system, on the A2. It's ambitiously signed to the Channel Tunnel from here now (it always used to be Maidstone and Folkestone). However, if you want to go anywhere beyond the M25 from here, I'd advise using the A2 and M25 J2-3 - it cuts out most of the traffic lights and is usually quicker.
It trundles along Loampit Hill and Vale to Lewisham, where the A21 branches off at a brand new roundabout. Then along Lewisham High Street itself, past the massive site of the old Army and Navy (which was still unfilled the last time I looked), and onto the Lee High Road. This is the really boring bit - you go past mile after mile of tatty London shops selling kebabs and haircuts, with your journey frequently broken by red traffic lights. At Sutcliffe Park, the A20 veers off to the right while the A210 chugs along to Eltham. (The A2213 Kidbrooke Park Road used to be signed to "The North (A1)(M1)" and all the rest, but those days are long gone now). We're now on dual-carriageway road lined by 30s semis, and there's still a 40mph limit. The A20 meets the South Circular Road at a roundabout, and continues. The traffic lights keep coming, so don't get any ideas that this might be a good road because of the dual carriageway. I breathe a large sigh of relief every time I go past the Fiveways junction (B263) which is the last set of lights!
Now the A20 bypasses Sidcup, then Foots Cray — the Foots Cray bit is relatively recent (last 15 years I think), then there's a sweeping curve round onto the Swanley bypass. This is a great bit of road, though sadly surfaced in concrete. An extra lane pops up in the middle of the existing two, and you know you're well and truly out of town (coming the other way, this is the first view of the Canary Wharf tower IIRC). At the end of the wonderful Swanley bypass, there used to be a simple junction where the B2173 (old A20 through Swanley) joined. This was all changed when the M20 and M25 made it here (very early 1980s). Now there's a TOTSO, as if you stay on the carriageway you end up on the M20, and the junction is a roundabout with exits for the B2173, A20 (E) and slip roads to the A20 (W), M20 and M25 (as well as extra sliproads linking the northern M25 with the M20).
Swanley - Maidstone
From here until Folkestone the A20 is living under the shadow of the M20, and the traffic is accordingly less. We travel around the Farningham bypass (built in the 1920s I think) and up Gorse Hill. This used to be called Death Hill, but was renamed about 30 years ago, presumably because they didn't want to scare drivers! We go past Brands Hatch motor racing circuit, which hasn't seen a F1 race for a good 15 years now. All this bit of A20 used to be 3-lane with a suicide lane down the middle. It was taken out about 10 years ago, and there's now crosshatching between the two lanes. After the uninspiring village of West Kingsdown, we pass under the M20. The M20 used to stop here for a while, before the section on Wrotham Hill was built, and there were slip roads to the north/west bound M20. There's no trace of them now, as far as I can see.
After a few miles we get to the top of Wrotham Hill on the top of the North Downs (where there's a radio mast with lights on you can see from miles around), and the M20 eastbound offslip meets us at a small roundabout. Now there's a lovely straight bit of road downhill with great views over the Weald of Kent, still three lanes, down to the next roundabout with the A227. Mind you, it's not lovely when you're aquaplaning down it as I did once... The whole of the Wrotham area was transfigured in the early 80s to make way for the M20. We encounter M26 J2A after a while, which traffic to and from the eastern M20 must use - for a while this was effectively the western limit of the M20. After the A25 junction at Wrotham Heath, there's a once-good bit of road which was ruined about a year ago when the middle lane was removed, cross-hatching put in and a 50mph speed limit put in on bits of it. Then through Leybourne to meet the A228 at a set of traffic lights (ex-roundabout), which connects with M20 J4.
From here until M20 J8 I wouldn't recommend the A20 as an alternative to the M20 even if there's an accident: Maidstone and environs have crept westwards to here, and this is all traffic lights and 30-40mph limits. I remember when there was only one set of traffic lights between the A228 and Maidstone, and I'm not that old... Anyway, the A20 goes through Ditton and the south of Aylesford, and through Royal British Legion Village, where the poppies are made, to a roundabout which connects with M20 J5.
M20 J5-8 is the Maidstone bypass bit of the M20, which was built first, and was originally numbered A20(M). This meant that the A20 through Maidstone had to be renumbered, and the authorities chose the snappy A2020. When the rest of the M20 came along, however, the Maidstone bypass was subsumed into it, and the A20 regained its number through the town. In Maidstone itself I think there's now a slight break in the A20, now that High Street and King Street are for buses only. A20 traffic should use the A229 and Wat Tyler (as in Peasants' Revolt; he came from Maidstone) Way to get back on. Then out through Bearsted to M20 J8.
Maidstone - Dover
For a long time, there was a gap in the M20 between J8 and J9; this was only completed in 1991, and so before this all M20 traffic had to trundle along the A20 between the two sections (or use the A249/M2/A2 if they were heading for Dover). This used to be an awfully congested section, therefore, and very tedious to drive along. It's a lot better now - you can enjoy the fast roads and the countryside (hopefully the CTRL hasn't put paid to too much of that). Look for Leeds Castle on your right, by the way. (It's named after a small village nearby, and has nothing to do with its urban Yorkshire namesake.)
After passing through Harrietsham village it is a reasonably fast journey courtesy of the Lenham bypass where a cross can be observed carved into the face of the North Downs. The dual carriageway just before Charing has been tamed into one lane each side now and the village that follows is famous because a cross-bearing pilgrimage to London gave a certain area the now familiar name of Charing Cross.
The Channel Tunnel Rail Link has shifted the course of the road a little on the way to Ashford, just as it did just before Harrietsham. The dual carriageway leading into the town now has a roundabout slapped in the middle of it to serve one of Ashford's many new housing developments. At Ashford proper, we get to a big roundabout, and the A20 disappears for a breather (it zips across to M20 J9).
The original route of the A20 through Ashford has now been stolen by the A292. The next incarnation of the A20, the bypass, used to go along Simone Weil Ave, and onto what's now the M20 (there isn't a junction there now). The non-trunk, non-primary A20 reappears in earnest at M20 J10.
From now on the road gets much quieter, passing through the villages of Smeeth and Sellindge. Then a sharp turn to the left at the A261, which goes into Hythe. This is the site of England's first Motel. After this, the road runs up to M20 J11 and the B2068 - to get back onto the A20 you have to double back on yourself and take a left turn to join up with the original route.
There's a bridge over the M20 again and a sharp right hand turn, then it's off towards the Channel Tunnel Terminal. You can get to it from the A20 as well as M20 J11A. After crossing the M20 yet again, the road runs through the middle of Cheriton before doing a sharp left onto Cherry Garden Avenue to meet up with the terminus of the M20 at junction 13. The A259 also terminates here, although originally it was the other way round with the A20 finishing at Folkestone and the A259 carrying onto Dover. The old road is now the B2011, which is a number recycled from the Malling area.
After this, the A20 takes up the motorway traffic which it left behind at J1. The A20 from Folkestone to Dover is now a bypass of the old route via an awful hill (named Dover Hill on the map here) and through Capel. The new route dives into some exciting tunnels in Sugarloaf Hill (this bit is a "secret motorway", with pedestrian, etc. restrictions), and has grade-separated junctions with the A260 and the B2011.
The bit into Dover is now great fun to drive along. Where the old route used to go past Dover Priory station and into town along a slow single-carriageway road, the new route dives down to the coast by Shakespeare Cliff (the point at which the Channel Tunnel leaves the shore) with some great views of the ports. The A20 finally calls it a day at the Eastern Docks, where it meets its big brother you thought we'd left behind in New Cross, the A2.
Original Author(s): Tom, Adam Colton