Replacing the Circle line with a moving walkway is an idea that's been around for decades.
Most recently Architecture firm NBBJ wanted to strip the Circle Line of its running tracks and install a series of moving walkways through the tunnels.
Three parallel walkways would move progressively faster, allowing passengers to reach a top speed of 15 miles per hour. Walking along this belt would supposedly be quicker than current Circle Line trains, which have to stop and start at each station.
Similar schemes have been floating around for well over a century.
American Alfred Speer is credited with proposing the first moving walkway in 1873. He later refined the notion into an unrealised system for Manhattan that would have used three parallel belts, with the fastest running at 19mph — almost identical to the NBBJ scheme. A scheme for London was considered as early as 1894. It, too, would have used the Circle Line tunnels, as this press cutting from the Western Gazette shows:
The notion was then adopted and developed by HG Wells. His novel The Sleeper Awakes (1899) employs the now-familiar plot device of a man waking from a coma a century after he fell asleep. Our proponent, Graham, finds London altered beyond recognition. In one chapter, he marvels at the dominant form of transport:
"But this roadway was three hundred feet across, and it moved; it moved, all save the middle, the lowest part. For a moment, the motion dazzled his mind. Then he understood. Under the balcony this extraordinary roadway ran swiftly to Graham's right, an endless flow rushing along as fast as a nineteenth century express train, an endless platform of narrow transverse overlapping slats with little interspaces that permitted it to follow the curvatures of the street. Upon it were seats, and here and there little kiosks, but they swept by too swiftly for him to see what might be therein. From this nearest and swiftest platform a series of others descended to the centre of the space. Each moved to the right, each perceptibly slower than the one above it, but the difference in pace was small enough to permit anyone to step from any platform to the one adjacent, and so walk uninterruptedly from the swiftest to the motionless middle way. Beyond this middle way was another series of endless platforms rushing with varying pace to Graham's left. And seated in crowds upon the two widest and swiftest platforms, or stepping from one to another down the steps, or swarming over the central space, was an innumerable and wonderfully diversified multitude of people."
In real life, moving walkways were first demonstrated at the 1893 World’s Columbian Exposition in Chicago — though more as a fairground attraction than a practical transport mode. The idea has since been put into practice only occasionally, yet has become a staple of future gazers. Not long after Wells’ novel, for example, T Baron Russell had this to say:
“Cities will be provided with moving street-ways, always in action at two or more speeds; and we shall have learned to hop on and off the lowest speed from the stationary pavement, and from the lower speeds to the higher, without danger. When streets cross, one rolling roadway will rise in a curve over the other. There will be no vehicular traffic at all in cities of any size; all the transportation will be done by the roads’ own motion.”
Despite promising trials in Paris and other cities, nothing quite like these moving walkways has ever been built in London. The idea was briefly revived in the 1960s, when architect Geoffrey Jellicoe proposed a futuristic city on the western outskirts of London. His 'Motopia' would have seen rooftop motorways and moving walkways for pedestrians. Needless to say, it didn't happen. The nearest approximation to the walkways would be the travelators commonly found in airports, and at Bank and Waterloo tube stations — none of which has the complex interlacing of multiple tracks arriving from different directions.
When it comes to moving walkways, NBBJ is just the latest firm on a long conveyor belt of dreamers. While the idea is an intriguing thought experiment, it would probably encounter too many practical issues to ever become a reality.