Architectural firm NBBJ has proposed a new three-lane moving sidewalk (or for the Brits, a travelator) system to replace 17-miles of the London Underground in a bid to decrease travel times and transport more people around London.

Earlier this year, a plans for a London underground bike complex was ridiculed by the Guardian in its attempt to reduce congestion despite it winning best conceptual project at the London Planning Awards.

With that in mind, NBBJ have boldly chosen to submit their idea which would feature three moving walkways traveling at different speeds. The nearest walkway to an entry platform would travel at a leisurely three miles per hour, accelerating to 9mph in lit tunnels. The project’s main advantage over the current rail-based system, designers claim, is that the walkway wouldn’t have to stop at the station—the ever moving track being slow enough for people to hop on and hop off.

The idea could have potential to be dangerous with the sheer mass of people it aims to take on, not to mention the cost implications this would have for Transport for London. Tearing up track and making the Circle line’s dark and dingy tunnels safe (let alone nice) to walk down would be no mean (or cheap) feat.

Moving walkways do already exist in the London Underground system, in fact they have been present at Bank station for 55 years. NBBJ’s proposal can also be seen as following on from the Trottoir roulant rapide (“fast moving walkway”) at the Métro station Montparnasse-Bienvenüe in Paris. Nicknamed the “TGV,” the Parisian example failed to garner success in the French capital, as the the Paris metro has had to pay out injury compensation in several cases.

According to the BBC, many users of the TGV quickly ran on the moving surface despite a loudspeaker barking orders of “keep your feet flat on the ground, keep your feet flat on the ground.” The failed project was replaced by a more conventional walkway in 2009.

The effectiveness of travelators is also up for debate. In 2009 (a bad year for travelators it seems) the Daily Telegraph reported that research about moving walkways in airports indicated they actually slowed people down and that the time advantage was minimal.

NBBJ still advocates the health benefits of walking between stations that such a moving walkway system might provide.