SkyCycle (proposed transport project)
SkyCycle was a proposed transport infrastructure project for London of a 219-kilometre (136 mi) network of elevated cycle paths above train tracks. The routes would have had a width of up to 15 metres (49 ft), and be accessed by over 200 ramps throughout the city, subject to a toll of £1.
Source: Wikipedia — SkyCycle (proposed transport project) (CC BY-SA 4.0)