If, at some point in the future, you find yourself walking through a London underground tunnel rather than riding in a train, it may not be because something's gone terribly wrong.

Instead, you may be moving effortlessly through the city on a highway of moving sidewalks, getting about as quickly as you would on a train but without the hassle of schedules, fares, and crowds.

This vision of the future comes from the London architecture firm NBBJ, which came up with that funky skyscraper that doesn't cast a shadow. The firm developed the concept for an ideas competition New London Architecture hosted to generate "hypothetical but realistic proposals to make London a better place."

NBBJ

The 17-mile Circle Line is a loop through central London with a reputation for being slow, delayed, and clogged with tourists. It carries 114 million people each year, but can run no more than eight trains at a time, each limited to 20 mph. NBBJ thinks walking would be faster—if you give people a little help.

First, you get rid of the tracks and replace them with three adjacent moving sidewalks (which, by the way, Britons call "travelators"). Passengers enter through stations and pay fares the same way (some things never change), but instead of waiting for a train, they step off the platform onto the outermost lane, which moves at 3 mph—a typical walking speed.

As on the highway, things speed up as you move to the right (remember it's Britain, where they drive on the other side). The middle lane's going 6 mph, and the third zips along at a brisk 9 mph.

In the tunnels between stations, each lane could speed up. (ThyssenKrupp has figured out how to make a variable speed walkway using magnetic levitation and overlapping plates. It's quite loud and totally awesome, and Toronto's Pearson airport has been using a variation on the tech since 2007.) At max speed, a Londoner or tourist could be walking at 15 mph. Without the need to stop at each station, NBBJ says, you could make the full circle in 55 minutes—five minutes faster than the train.

NBBJ

More important than speed, though, is eliminating the train's most annoying aspect: overcrowding. With the walkways, you can fill the entire tunnel with people, and not lose space to spread out trains. As a result, the system could carry three times as many people. "The real benefit is the capacity," says Christian Coop, NBBJ's design director.

That's the "realistic" part of the idea: using proven technology (moving sidewalks) in a proven way (a highway lane system) to fix a vexing problem.

The idea has real solid potential. Christian Coop, NBBJ Design Director

Oh, the downsides. First off, it's unclear how much this system would cost to build or operate, or how much energy it would use. That's because it's still in the early concept phase, Coop says, and the team hasn't bothered doing the math yet.

The bigger problem is any system based on moving sidewalks isn't friendly to people who don't walk well, or at all. One rendering shows a person in a wheelchair (other renderings include Daniel Craig, Queen Elizabeth II, and Elvis) and chairs set up in the fastest lane. But it's really easy—like super easy—to imagine people having trouble moving between lanes, or stumbling as they get on and off.

Plus, anyone who's been to an airport knows these things break down. A nuisance when you're changing flights could make getting from Notting Hill to the Tower of London a disaster.

Still, Coop says "the idea has real solid potential," and that it's been well-received so far. It likely won't see the artificial light of an underground tunnel, but the concept is worth something in its own right. "Usually an idea just leads to another idea," Coop says. Maybe the next one will fix London.