We’ve had suggestions for a floating cycle highway along London's river Thames and and another in the sky. Now a quirky scheme has been proposed to enable people to travel around London with ease – a moving walkway following the city’s underground Tube train network.

The concept, designed by architects at NBBJ, would reinvigorate urban mobility in the capital, which suffers from overcrowding during rush hour.

The studio proposes replacing some trains with three side-by-side electronic walkways – similar to those at airports – which move at varying speeds around the 17-mile (27km) Circle Line.

Commuters would enter at the slowest speed of 3mph (4kph)and slowly increase their pace moving outwards onto the fastest lane, which would reach a top speed of 15mph (24kph).

NBBJ say that when added to the average walking pace of 3mph, pedestrians would actually move faster on foot than today’s Circle Line trains, which travel at 20mph (32kmph) but have to stop at stations.

In a statement, the studio said: “The result would be considerably quicker, more enjoyable and healthier journeys.”

In a separate development, Transport for London has published a new map showing the time it takes to walk above ground between almost all of the stations on the Underground network, in a bid to get more people to walk instead of taking the train. That move followed hot on the heels of a University of California study showing that cities which foster physical activity enjoy economic benefits such as higher retail revenues and lower healthcare and crime costs.

NBBJ, which is based in London, is developing a reputation for its outside-the-box thinking. In March the firm revealed their concept for ‘shadowless skyscrapers’; a way of utilising mirrors and design software to reflect dispersed sunlight onto the streets below tall buildings.

NBBJ skyscrapers cast light instead of shadows