I have a friend who's a Londoner (or was), and she says that the Tube is very nice. If I may ask, what are the fares? In DC they are quite high: from $1.80 to $5.50 for a one-way ride, depending on the distance and time of day, and the real cost is twice that, since it's 50% subsidized and taxpayers pay the rest.
See http://www.tfl.gov.uk/tickets/14416.aspx for fares and http://www.tfl.gov.uk/assets/downloads/london-rail-and-tube-services-map.pdf for a map of all Tube, rail and tram lines.
£2.10 for a single journey in the central zone (any time).
£1.60 for a single short-ish journey not in the central zone (peak time).
£3 for a very long journey off-peak, £5 at peak (zone 6 to zone 1).
Bus: Any bus (or tram) journey is £1.40.
There is an automatic limit to what you pay if you use the contactless payment card (which everyone does), see the web page ("price cap"). There is a lower limit for only using buses or trams.
Road: driving between 7h-19h within (roughly) zone 1 costs £10.
I can't find reliable figures on the amount of subsidy. It seems to be mostly of interest to right-wing crackpots. The revenue from the £10 congestion charge is spent on public transport.
Fares have increased significantly with the current mayor, I think he has shifted what the subsidy pays for.