Check out this crazy plan to turn London's abandoned tunnels into cycle paths

A concept to turn London's abandoned Underground tunnels into cycle paths and walkways sounds outrageous, but is "being taken seriously" by some people, according to The Guardian's Feargus O'Sullivan. 

The London Underline, proposed by the San Francisco-based design agency Gensler, would turn London's disused underground spaces into a network of pedestrian and cycle paths. The system would even convert the friction created by footsteps and bike tyres into electricity. So it's sustainable, too. 

The proposal just won an award for Best Conceptual Project at the London Planning Awards - so while far-out, some people believe the London Underline is a viable answer to London's congestion problem. The capital's railway system is already strained and London's population keeps growing.

In a press release, Gensler explains that the "untapped surplus of disused space" could also be home to retail space and event venues.

Here's what that might look like:

According to Gensler, the tunnels would all powered by PaveGen, an organisation that produces kinetic energy system that converts footsteps into electricity. Transport consultancy firm Momentum also helped with the plans.

"Gensler's proposal brings back an ignored part of the city," Gensler designer Travor To said on the company website. "By harnessing the kinetic energy of every one's footsteps, a whole new urban space is unlocked underneath the city."

O'Sullivan talks about some of the areas that might be transformed. There's a defunct branch of the Piccadilly Line that runs from Holborn to Aldwych, and an "even longer artery" that connects Green Park to Charing Cross. He says these are the two Gensler has a "serious eye on."

There's no timeframe for when these underground cycle paths could become a reality, but here's video explaining Gensler's vision for the future: