Mind the gap

I have heard "mind the gap" at Queenstown Road, on a train not scheduled to call there and with a gap of four running lines between the train and the nearest platform!

Rolling stock handed-ness

Historically most Underground rolling stock couplings were "handed" - a left handed coupling ("A-end") could only couple to a right handed one ("D-end"), and each unit had one of each. (Ambidextrous couplings need some connections to be duplicated or stacked one above the other, both difficult to arrange in the very limited space available on the end of a Tube car).

A common orientation made it easier to arrange stock transfers between lines. (And yes, the loops at Hainault, Kennington and Heathrow do complicate matters).

Castles in Greater London

I suppose it depends on your definitions of "castle", but surely Baynard's Castle must count? (There's not much left of it, but then the same can be said of the one in Ruislip).

Caesars Camp on Wimbledon Common? (Actually misnamed, as it is Iron Age)
Does Jack Straw's Castle count?

One would not expect to find a Norman castle in the Domesday Book, which was essentially a stocktaking exercise of the assets seized/inherited by William the Conquerer in 1066. And certainly anything built in Middlesex in the 9th century wouldn't be Norman - it was part of the Kingdom of Mercia at the time.

Kingston has a "Castle Street" but there is no castle - the street is apparently named after a Mr Castle. It also has a housing development on a former barracks (of which the gatehouse remains), called The Keep.

Ongar zero datum

The datum point of Ongar was used because anywhere else (except Chesham) would have required some points to be negative.

The Northern City Line still used miles from Moorgate in 1975 (see the Official Inquiry into the crash). By 1972 the NCL was not directly connected to the rest of the system - the Highgate route had been closed in 1971 so stock transfers had to run via Kings Cross and the "Widened Lines". Neither Brill nor Verney Junction were part of the Underground in 1972.

Wembley to Shortlands

Wembley and Shortlands are both in Zone 4, so not touching in and out for the second leg wouldn't actually save very much - only the "TOC premium" (and he would save even more - legally! - by going via Clapham Junction).

A Zone 4-Zone 4 journey made is allowed more time than a Zone 4-Zone 1 journey actually paid for. You could be over time at Elephant, and back within time at Bromley South. (although non stop services such as Victoria - Bromley South, London Bridge - East Croydon or Waterloo- Surbiton are better bets for pulling that trick)

National Park Cities

Three National Parks have cities, or parts of cities in them. Pembrokeshire Coast (St Davids), South Downs (Winchester and Brighton & Hove), Peak District (Sheffield).

La petite Ceinture

Most of a re-opened petite Ceinture would duplicate Metro Lines 2 and 6, which shadow it very closely. However, part of it has been re-used in RER Line "C".

Carbon dioxide

Most of the CO2 used in fizzy drinks is a byproduct of fermentation processes, mainly in the brewing industry, and would otherwise just be vented to the atmosphere anyway.

Crowd support

Crowd support at football matches is probably a factor but other factors may also be involved, such as familiar surroundings (both in the pitch and in the dressing room), acclimatisation, and not having to travel a long distance to the fixture. It would be interesting to see whether there is still a "home advantage" in games that have been played behind closed doors.

Late station openings

Pimlico is a more recent example of an Underground station opening after the line it is on. Pudding Mill Lane and Canary Wharf are examples on the DLR. (From Day 1 the automatic trains used to stop there, even though there was no trace of even a platform).

Crossrail to Heathrow

Although the Tube map pretends they don't exist, Finsbury Park has direct services to both Moorgate and Farringdon, both giving connections to Crossrail. In the short term a change at Paddington will be needed for Heathrow, but from the end of next year (if all goes to plan) there will be direct trains from both Farringdon and Moorgate to Heathrow.

Finsbury Park to Heathrow by Piccadilly Line is 65 minutes, via Farringdon will be about 45.

And of course it's not just about Heathrow - connections to East London and Docklands from north London will be much faster too.

Population pyramids

There was a marked dip in the birthrate from the early 1990s to a minimum in 2003 (15 year olds), but I haven't noticed a National Teenager Shortage.

The rate has been declining again since 2012.