CITY LIVING - WALKWAYS

High-Speed Moving Walkways (AKA, Slidewalks)
(by Troubadour of skscraperpage forum)

There have been a number of experiments with high-speed moving walkways over the past few decades (largely in Europe) - all of them for relatively short distances inside transportation terminals, and none of them successful. Nevertheless, the technology has proven its enduring conceptual appeal by the fact that experiments keep happening, and innovative new approaches explored.

I. The Past & Technical Challenges

Now, one's definition of "high speed" has to be pretty humble when talking about the trials that have been done. The fastest attempted so far involved two systems - one in Geneva in the '70s and one in Paris in the '80s - that took riders at 9 mph, or about three times a brisk but unhurried walking pace. The key challenge with these and the other systems, as you can imagine, was in acceleration and deceleration.

Essentially, it comes down to being able to keep your balance in the transitions, which in practical terms means handholds are necessary even if transitions are broken up into multiple, gradual steps. This is not a simple thing, because moving handholds are mostly known through experience with escalators, in which case they are belts moving along unbroken sidewalls. But many of the designs for moving walkways relied on parallel strips moving at different speeds, which means people would have to move horizontally, breaking contact with one handhold and passing through a gap in the other.

Such gaps would be a big problem - while in transition, the person would have no stabilizing hold, having let go of the opposite rail and passing across gaps in the intermediate handrail big enough to safely cross (which means they wouldn't be within reach during the transition). But even if there were only two parallel strips and no intermediate handrail - thus allowing people who are safely on either side to rely on one hold exclusively - the line between the belts would be dangerous: Falling on it could easily shred skin, prevent a person from getting up and regaining their balance, and cause chain-reaction pedestrian pileups.

Another approach has tread plates independent of each other that can accelerate mid-course by spreading out or shift laterally into a faster lane. While this could allow each tread plate to carry its own handholds with it, the underlying mechanics of the plates' motions proved complex and unreliable. However, the principle of single-track, accordion-like behavior being utilized for acceleration and deceleration was found potentially practical for belt-fed systems.

On a personal note, I will say that in my modest experience with (slow) moving walkways, my main issue was that if I walked forward on them rather than standing still, the scenery passed to the side much faster than my brain was telling my gut to expect, so there was a danger of queasiness if I didn't stay focused straight ahead. This probably would not be an issue at much higher speeds, since it would be more like walking down the aisle of a train than merely seeing things moving by at jogging speeds while you're merely walking.

Another issue is that for any significant distance, having the movement of the entire system depend on the functioning of the entire length of the walkway increases the likelihood of failure. So implementing moving walkways as a general transportation method for cities has not looked very practical - and yet its promise remains.

II. The Present & Current Implementations

Supposedly, there is currently a "high-speed" (4.3 mph) walkway at Toronto Pearson airport that relies on accordion-like expansion of the beltway for acceleration, followed by contraction near the end for deceleration. However, it appears the effect is very modest. Virtually every moving walkway currently in use - most of them are in airports, luxury shopping malls, or large casinos - is merely an "augmented walking" system that roughly doubles your speed if you walk forward normally on it. They are not, in other words, real transportation systems so much as minor conveniences if you would rather get from Building A to Building B in 2 minutes rather than 4.

Paris Metro had installed a high-speed walkway at Montparnasse a few years ago, but abandoned it due to the frequency of accidents, and the apparent need for ham-handed restrictions like having personnel available whose only job was to stop people from getting on it unless they had at least one hand free to hold on to the rail - basically, they were forced to act as roller-coaster attendants for something that was supposed to be a public transit system.

III. The Future & Potential Applications

We can imagine some conceptually trivial solutions to these problems that do not appear to have been tried yet, although I don't doubt there are real technical challenges involved: For instance, with two-parallel-track belt systems, there could be hanging handholds such as in subways or buses that are projected by arms attached to the handrails on opposite sides. In this way, you could "monkey-bar" your way from one overhead handhold to the next until you are at the transition, and then grab a faster-moving hold just as you step across, not letting go of you original hold until you'd grasped the new one.

Falling on the transition between tracks could still be painful, but the differential motion of the belts in the presence of other people who are strongly stabilized would just force you on to one or the other belts. People would have to leave the walkway before the projecting arms could be folded back into the belt, but that doesn't seem especially complex in concept - just feed the tread portion of the belt under the ground well before the arms go under, and then have them both loop around beneath the ground some distance after that.

Another idea that I haven't heard about being tried would be angled aisles of strong elastic webbing with flexible vertical struts. This would allow for more than two tracks in a parallel-track system, since you wouldn't need overhead handholds. In fact, perhaps this webbing folds from the vertical into seats in the middle of the track so people going long distances can sit down. Folding the webs at the end of the track would be no bother, and cleaning would be easier than with fabric seat cushions like in buses or trains.

With safety features like this, it seems more likely that walkways could achieve significantly higher speeds, with several transitional tracks that would otherwise not be safe to cross. And, of course, with higher speeds, that naturally leads to a question about what greater distances might be practicable, which in turn leads us back to the problem of the whole pathway being dependent on a single system to function. So clearly without some additional changes, the safety features would not extend distances to more than a few times what they already are, because the system would grow increasingly balky the longer you made the pathway.

Enter maglev walkways: Magnetic levitation of the tread surface a few millimeters above the active surface. If the power goes out, the system doesn't jerk to a stop and send everyone tumbling - it just no longer pushes/pulls it forward, so the tread surface coasts to a stop, remaining levitated (or at least electrically lubricated) by the properties of the underside materials.

Since you've separated the tread from direct contact with the systems moving it, it could be fail-safed - i.e., any failure of those systems would only be reflected in a gradual reduction in speed averaged over the entire walkway, along with a predictable and manageable increase in shear and/or tension forces on the tread near where the failure occurs. This wouldn't guard against direct obstructions of the tread itself, but protecting a long strip of relatively thin, solid, simple material with no moving parts is actually a lot easier mechanically than dealing with machinery.

As to the remaining safety objections, I would simply ask this: Consider how many pedestrians die every year interacting with automobiles in ways that are totally unnecessary, both in terms of the people using them and the people who die by them. Millions are forced into cars and dangerous freeways purely by the design of their cities and regions, and people who walk anyway are then forced to deal with the consequences. What if there were a much cheaper solution to this problem than subways; a more accessible and regular solution than buses; and a more flexible solution than light rail?

If you could just walk out your door and within a few dozen steps and thirty seconds' time later be going 30 mph the whole of your trip (when not changing walkways), would you actually wait 10 minutes for a bus, train, or subway that constantly starts and stops, and has to flow with traffic? If you could have the pedestrian experience over much larger distances, would you still rely on a car for those distances? Would you still accept the relatively acute dangers, discomforts, and inconveniences of bicycle transit? There is clearly a significant urban niche for high-speed moving sidewalks if the safety and reliability issues can be reasonably dealt with.