The delicate balance between escalator speed, capacity, & safety (CityMonitor)

If we want to increase escalator capacity, why don’t we just run them faster? Well, here’s why.

On long escalators, the vast majority of people don’t want to walk. Thus, huge queues build up at the bottom of the escalator as large numbers of people try to squeeze onto the right-hand side, so that they can stand in line as they chug slowly upwards at max capacity.

There is a potential solution – one that’s likely been suggested by logistics all over the world every time they’ve found themselves in such mildly antagonising and incremental-delay-incurring situations: run things faster.

Theoretically, of course, this is possible. Escalator speeds vary a great deal anyway, even within London – those in shopping centres or department stores tend to run at about 0.5m per second, while the London Underground standard is 0.75m per second.

The escalator capacity solution

Looking further afield, city transport networks across the world run their escalators at all sorts of different speeds. New York City’s are considered slow, running at about 0.45m per second, while Prague, Stockholm, Beijing, Shanghai, and Guangzhou settle around 0.6m per second. Sydney, Singapore, and Seoul’s systems square up to London’s standard speed in the 0.75m per second region, with Seoul pushing ahead slightly at 0.78m per second. The trailblazer, though, is Hong Kong, whose escalators breeze along at 0.8m per second.

Unfortunately, a comparison isn’t that simple. London’s escalator steps are, as standard, 1m wide and 0.4m deep. Many of Hong Kong’s escalators are significantly narrower and not as deep. Whether that’s clever space-saving on Hong Kong’s part, or future-proofing by Transport for London, we may never know – but either way, it changes the rate at which steps reach the top, rendering direct comparisons based on speed alone impossible.

The escalator speed limit

What we can do instead is to look at a study carried out by four students from Hong Kong on the relationship between escalator speed in metro systems and “pace of life”. They described that metric as “the rate; speed and relative rapidity or density of experiences, meanings, perceptions, and activities”. They calculated it by combining economic, climate, employment, and population indices.

One of the things they did as part of that study is to conduct reasonably lengthy interviews with users of metro systems (principally the Hong Kong MTR) about their experiences of the escalators on that system, and how that related to their impression of the city’s “pace of life”. One businesswoman in her mid-twenties interviews for the study said that “Hong Kong people are used to the fast”; but most of the non-locals that they spoke to, mostly from mainland China, said that the escalators on the Hong Kong MTR were “too fast”.

Such comments highlight one of the biggest problems with running escalators faster. A study by Paul Davis and Goutam Dutta has already shown that the presence of non-commuters decreases capacity on London’s escalators. Meanwhile, an experiment with variable-speed escalators in New York ended up with an Indian visitor falling over.

There is quite obviously a danger to be taken into account if you’re going to start running escalators at 0.8m per second or faster. The queues at the bottom might be shorter most of the time if said escalators are whizzing passengers upwards at speed – but they’ll likely be longer while the paramedics try and reach the elderly man who’s tumbled 15m down an up escalator.

For those less interested in actual human health and welfare, and more interested in the technical side of running large transport networks, there’s another problem with running such escalators at speed. The average walking speed is around 1.3m per second. If you take the running speed of London Underground escalators – 0.75m per second – and the rate at which people generally ascend the steps if they’re walking – around 0.7m per second – you end with a speed of 1.45m per second.

So people walking up escalators are actually travelling slightly faster than they do the rest of the time. And that’s a problem. When it’s only an incremental difference (0.15m per second), it leads to nothing more dangerous than the awkward super-walk that people do for the first few seconds after walking off the end of an escalator.

But when there’s a bigger difference in speed, it can cause major problems. Either, people trip over their own feet trying how to remember how to walk on non-moving ground, and cause a capacity-reducing pile-up in the process; or people stop at the top of the escalator to prepare themselves for walking on non-moving ground. And cause a capacity-reducing pile-up in the process.

Essentially, speeding up escalators causes more problems than it solves.

Starting again

Fortunately, researchers Davis and Dutta do come up with some more sensible alternatives. Unfortunately, these are the sort of drastic changes that are much easier to implement if you haven’t built your metro system yet than they are if you’re trying to unclog a jam-packed 150-year-old system.

Of the many London Underground escalators they studied, the researchers found that those with the highest peak-time capacity were escalators with open, orderly approaches, not impeded by awkward corners and cross-flow confusions.

They found that having a corridor between the platform and the escalators acts as a filter for passengers alighting a train, improving capacity as passengers naturally filter out into two lines – one for walking and one for standing – in an orderly way (rather than the human crush you get when you come straight off the platform, turn a corner, and suddenly there’s an escalator).

Interestingly, single escalators have a higher capacity than double escalators, because passengers don’t dither trying to work out which escalator to take.

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