What is London's longest alphabetical train journey?
(this, of course, depends on what you mean by 'alphabetical journey')
Stations beginning A, B, C, D etc
Only nine tube stations start with the letter A.
Only one of these (Arnos Grove) is adjacent to a tube station starting with the letter B (Bounds Green).
But the next station (Wood Green) starts with a W, not a C, so that's the end of the chain.
The longest alphabetical journey on the tube is therefore Arnos Grove → Bounds Green.
So that's a disappointing start.
If you extend the search to the entire tube map, four more stations start with A.
But none of these are next to a station starting with B.
Purely in terms of probability, that's not really a surprise.
If you're happy to accept tram stops, there are three more A→B journeys. Addiscombe → Blackhorse Lane, Avenue Road → Birkbeck, Avenue Road → Beckenham Road
But there are still no adjacent Cs.
If you extend the search to all of London railways, hurrah, there's one better success. Albany Park → Bexley → Crayford
And if you allow any stations within the Oyster zone, hurrah, that chain gets even better. Albany Park → Bexley → Crayford → Dartford
Across the whole of the rest of the UK rail network, only one other chain of stations matches that.
It's up in Scotland, on the line between Edinburgh and Glasgow. Armadale → Blackridge → Caldercruix → Drumgelloch
But A-D is the very best we can do.
Stations beginning with consecutive letters
What if the first station can start with any letter, not just A?
I can find only one chain of three consecutive alphabetical tube stations. Ravenscourt Park → Stamford Brook → Turnham Green
Even changing trains mid-journey doesn't add any more to the list.
The wider tube map, adding DLR, tram and Overground, offers nothing as good.
Throw in the whole of the London rail network and there are a couple more chains of three. Lee → Mottingham → New Eltham Richmond → St Margarets → Twickenham
But three stations is London's maximum, which is somewhat disappointing (unless you know better).
Outside London, here's a four in South Wales (but I can't find a five). Barry Docks → Cadoxton → Dinas Powis → Eastbrook
Stations containing consecutive letters
Can we find consecutive tube stations containing A, then B, then C, then D, etc?
Yes we can. Here are some chains of five.
Fulham Broadway → West Brompton → Earl's Court → Gloucester Road → South Kensington
Edgware → Burnt Oak → Colindale → Hendon Central → Brent Cross
Hampstead → Belsize Park → Chalk Farm → Camden Town → Mornington Crescent
Those are all without changing trains.
Allow changing trains, and it's possible to get to nine.
Chancery Lane → Holborn → Tottenham Court Road → Goodge Street → Warren Street → Oxford Circus → Green Park → Hyde Park Corner → Knightsbridge
Starting with K instead of A, here's a tube journey which hits the maximum of eleven.
Bank → Liverpool Street → Moorgate → Barbican → Farringdon → King's Cross St Pancras → Euston Square → Great Portland Street → Baker Street → Regent's Park → Oxford Circus
...and here's another.
Southwark → Waterloo → Westminster → Embankment → Charing Cross → Piccadilly Circus → Leicester Square → Tottenham Court Road → Goodge Street → Warren Street → Euston
Stations in alphabetical order
This should be easier.
In good news, two adjacent stations are always in alphabetical order, in one direction or the other.
In bad news, the next station only has a 50/50 chance of following on, and then again, and then again.
This is similar to flipping a coin until you get a different result, so a long chain isn't very likely.
Here are several examples of five consecutive tube stations in alphabetical order on the same line. Arsenal → Finsbury Park → Manor House → Turnpike Lane → Wood Green Baker Street → Edgware Road → Paddington→ Royal Oak → Westbourne Park Barons Court → Hammersmith → Ravenscourt Park → Stamford Brook → Turnham Green Bermondsey → London Bridge → Southwark → Waterloo → Westminster Borough → Elephant & Castle → Kennington → Oval → Stockwell Croxley → Moor Park → Northwood → Northwood Hills → Pinner Eastcote → Rayners Lane → South Harrow → Sudbury Hill → Sudbury Town Leyton → Leytonstone → Snaresbrook → South Woodford → Woodford
If TfL ever build the Metropolitan line extension there'll be a six.
Cassiobridge → Croxley → Moor Park → Northwood → Northwood Hills → Pinner
(but they won't, so there won't be)
If changing trains is allowed, I can get to six. Baker Street → Bond Street → Green Park → Hyde Park Corner → Knightsbridge → South Kensington
There is a genuine consecutive six on the Overground. Canonbury → Dalston Junction → Haggerston → Hoxton → Shoreditch High Street → Whitechapel
Here's a seven on the wider London rail map. Barnes → Mortlake → North Sheen → Richmond → St Margarets → Twickenham → Whitton
And if you allow changing trains, this is a ten. Beckenham Hill → Bellingham → Catford → Catford Bridge → Ladywell → Lewisham → Nunhead → Peckham Rye → Queens Road Peckham → Surrey Quays
(this assumes it's OK to use the interchange at Catford/Catford Bridge)
Across the whole country, using NationalRail, here are two sevens. Cardiff Central → Cardiff Queen Street → Cathays → Llandaf → Radyr → Taffs Well → Trefforest Estate Bidston → Birkenhead North → Birkenhead Park → Conway Park → Hamilton Square → James Street → Moorfields
Change at Moorfields and you can travel one more station to Sandhills, scoring eight.
And if you focus instead on stations stopped at during a single train journey, this is ten. Barry → Barry Docks → Cadoxton → Cardiff Central → Cardiff Queen Street → Cathays → Llandaf → Radyr → Taffs Well → Trefforest
That train journey is the 07:42 from Bridgend to Aberdare, and well done to Tom Forth for finding it.
He has a lot more of this kind of thing, computer-churned, over here.
(we'd best leave reverse alphabetical order for some other time)