- USD 17bn for 13.7 km of Second Avenue Subway in NYC, although several kms of tunnel have already been contructed in the 70s. http://nymag.com/nymetro/news/features/n_10109/ (March 29, 2004, according to Wikipedia)
- BP 16bn for 22 km central tunnel section of London Crossrail (Leftly, Mark (29 August 2010). "Crossrail delayed to save £1bn". The Independent on Sunday (London). according to Wikipedia)
- EUR 500m for 3 km of Stadtautobahn (only partly under ground) Gericht macht Weg frei für die A 100 – Wowereit begrüßt Urteil. Der Tagesspiegel, 10. Oktober 2012, abgerufen am 10. Oktober 2012.
On the other hand, the flying car has long been assumed as part of science fiction, yet there are no known technologies which make flying and landing over cities economically feasible for many:
- Helicopters require high amounts of energy just to float in the air, without even moving. Besides, they create lots of noise and wind and require too much safety room to fly.
- Planes are less inefficient, but only at high speeds. Most city-trips are shorter than a plane needs to get up to speed. Ultra-light (one-person) planes are very sensitive to wind and still require more space than available to start and land.
- Magnetic levitation also requires vast amounts of energy just to stay afloat. Besides, it can only float some mm or cm high, such that it still needs a full elevated roadway (such as a mono-rail).
Speaking about elevated roadways, those are actually much cheaper than tunnels be it for trains or for cars. However, elevated roadways have the disadvantage of carrying noise very far and creating so much shadow below that the road underneath feels like a tunnel. It is for this reason that elevated roadways (be it for trains or for private cars) are currently avoided in most western cities. Some are even torn down to be replaced by tunnels.
Thinking about the flying car, we have to ask ourselves how it is to be designed to avoid the pitfalls of elevated roadways. Number one: it has to be silent. Number two: it should not cast much shadow. As it turns out, we can grant both wishes economically using current technology. In my next post, I will introduce a means of airborne inner-city transport which is less noisy than the street traffic below and which casts not more shadow than a small multiple of the shadow cast by the people using it.