The London Underground has had a zonal fare system since the early 1980s, before which fares were based on far you travelled. In 1981 two overlapping central flat fare zones were created, called West End and City, and these were later combined to create zone 1. In 1982 further concentric fare boundaries were set at approximately three mile intervals, initially called zones 2, 3a, 3b and 3c, then 2, 3, 4 and 5.
In January 1991 zone 5 was split to create a new zone 6 around the edge of the capital, and a few tweaks have been made to boundaries since. That's not the subject of today's post. Today's post is about the small number of stations which exist in two zones, the stations on the boundaries.
Zone 1/2: 5 stations
Only four tube stations exist on the zone 1/2 boundary, i.e. on the edge of the West End/City zone defined over 30 years ago. I haven't managed to discover precisely when they gained this 1/2 designation, but all were in place around 20 years ago when the first zonal tube map was produced. The four stations include Notting Hill Gate and Earl's Court out west, Vauxhall and Elephant & Castle to the south, and nothing to the north or east. It's not immediately clear why these four stations were doubled up and not the others on the edge of the central zone. I checked the original central bus zone on a map, and it doesn't match up, so it isn't that.
Only one other station has been added since, and that's Hoxton, which was designated zone 1/2 when it opened on the Overground in 2010. It's only zone 1/2 because the Department of Transport forced TfL to nudge Shoreditch High Street into zone 1 to help pay for the extension, so Hoxton became part of the transition back to zone 2. It's a fairly pointless overlap too, because the only Zone 1 journey you can make from Hoxton is one stop to Shoreditch High Street, and that's walkable in less than ten minutes.
Zone 2/3: 29 stations
Here's where the number of boundary stations explodes, and there are dozens. Nine tube stations have been on the list since the start (Archway, Bromley-By-Bow, Clapham South, East Putney, Hampstead, Manor House, North Acton, Turnham Green and Willesden Green) These are all roughly three miles out from the original inner boundary, and fairly well spaced, but with Bromley-by-Bow the only overlapper to the east. It was joined in 1999 by the new station at North Greenwich, presumably designated zone 2/3 to stimulate Jubilee line journeys in both directions.
Four National Rail stations have always been part of both zones 2 and 3, specifically Clapton, Herne Hill, North Dulwich and Putney. These were joined in 2007 by Willesden Junction, nudged inwards from zone 3 when the Overground began, in order to prevent orbital journeys becoming unduly expensive. Hampstead Heath was rezoned at the same time, but it jumped directly from 3 to 2, because there's no point having a single overlap station at a non-interchange on an individual line.
Meanwhile on the DLR, the entire Lewisham extension straddled the edges of zones 2 and 3 when it opened in 1999 - that's Cutty Sark, Greenwich, Deptford Bridge, Elverson Road and Lewisham. Greenwich and Lewisham had previously been overlap stations for the National Rail network. Around the same time the DLR stations at East India and Pudding Mill Lane were shifted onto the zone 2/3 boundary, a direct reaction to the extension of the Jubilee line - previously both had been zone 3 only.
To round off this long list we come almost up to date, specifically January 2016, and the Mayor's decision to shift the centre of London fractionally east. This meant redesignating stations in the Lower Lea Valley from zone 3 to the zone 2/3 boundary, specifically to encourage growth by making people think they weren't quite as far away as they'd always been. The main beneficiary was Stratford, but West Ham and Canning Town also earned a place, resulting in the last four stations on the Jubilee line all being in both zones 2 and 3. Three intermediate DLR stations also got the upgrade, namely Star Lane, Abbey Road and Stratford High Street, plus the Olympic Park end of the line at Stratford International. And that's 29 stations in all, phew.
Zone 3/4: 11 stations
Just six tube stations lie on the zone 3/4 boundary, and as far as I can tell they've all been there since the start. Out east we have Leytonstone and East Ham, up north we have Hendon Central and Bounds Green, and to the southwest there's Kew Gardens and South Wimbledon. Again it's not immediately obvious why these have been chosen and others haven't, so for example one northern branch of the Northern line has an overlap, while the other jumps from East Finchley in 3 to Finchley Central in 4.
Four National Rail stations have always been on the 3/4 divide, specifically Hendon and Bowes Park to the north, and Manor Park and Woodgrange Park to the east. The latter is now part of the Overground, while Manor Park is currently part of TfL Rail, and will soon join Stratford as the only Crossrail stations to sit astride two zones. Finally there's Crystal Palace, which used to be in zone 4 but was moved to the 3/4 boundary in 2004, well before the Overground arrived.
Zone 4/5: 0 stations
There are no stations on the zone 4/5 boundary, not a single one. Goodness knows why not. For some reason every single station that exists close to the 4/5 dividing line was placed on one side or the other, and none ended up inbetween. "Which London fare zone boundary has no stations on it?" sounds like it should be a pub quiz question.
Zone 5/6: 1 station
But perhaps this is the better pub quiz question. "What's the only station on the zone 5/6 boundary?" You'd never know without scouring a tube map, but there it is on the Piccadilly line, the only outlier, it's Hatton Cross. This station opened well before 1991 when the original zone 5 was split into a 5 and a 6, so there's no obvious reason why it should be an anomaly. But it does mean you can get to almost-Heathrow-Airport by paying a little less than going all the way.
Zone 6/7: 1 station
There's only one of these as well. When London's fare zones were first created there were no stations on the outer boundary, and the far end of the Metropolitan line sat comfortably outside. Special zones A, B, C and D were eventually created to cope with Hertfordshire and Buckinghamshire, later simplified to 7, 8 and 9. The outermost overlap station was created in 1997 when Moor Park was moved from zone A to the edge of zone 6, specifically the 6/A boundary, now the more manageable 6/7. It's the only overlap station not to be in London, and the last of 47 overlap stations on my list. A fascinating set of reasons lie behind their perversely inconsistent spread.