Nudging people on the escalator

How to make people stand still to go faster

My very first visit to London left such a big impression on me that I can still recall it decades later. By far the most evocative memories are those of the London Underground: the scent of ozone and lubricant, the sounds of the sliding doors, the labyrinthine access tunnels and, of course, the escalators. The stoic discipline of the Londoners, standing on the right, walking on the left — as the signs everywhere urged travellers to do — was almost as baffling to a continental kid as the neat queues at every bus stop.

That segregation goes back nearly a century. In 1921, ten years after they were first introduced, passengers were first instructed by a recorded voice to stand on the right on escalators. Since then, stand on the right has become embedded in the collective psyche. It has guided generations of passengers smoothly through the underground system.

This is a great example of how a modest heuristic is able to provide both societal and individual value. If you’re in a hurry, you’re free to rush up on the left hand side and get to the top (or the bottom) a few seconds earlier. If not, just relax on the right and let the steps take the strain.

Except it seems it’s not that simple. The separation between walkers and standers may be on its last legs, so to speak. Earlier this week, an article on the gadget website Gizmodo reported on a study by public transport operator Transport for London (TfL). For six months, they had been monitoring the traffic flow on the escalators of Holborn tube station — one of London’s busiest — with passengers instructed to stand on both sides. This followed a 3-week experiment in November 2015.

In both cases, the evidence suggests that there are situations where it is actually better to stand still on both sides. The Independent’s headline read “It *is* faster to stand on the escalator rather than walk”, and in a slightly tongue-in-cheek way, they were right. The data showed that, when 40–60% of the people were walking, the escalator could handle maximum of 115 passengers per minute. But when everyone was standing, that went up to 151 passengers per minute.

More space

It is not hard to see why this is the case. The amount of space a walker needs is bigger than the requirement of a stander, so the capacity is lower when people are walking. You see this also on congested motorways: the safe distance between vehicles (and so the amount of road space each vehicle needs) is larger when the speed is higher. In many countries there are signs above each lane to restrict the speed when congestion looms. When everybody moves at the same, lower speed, more vehicles get through every minute.

In addition, keeping everyone driving at the same speed means there is little point in changing lanes. And that is good too, because lane-hopping has what economists would call a significant transaction cost. If someone squeezes in front of you, that forces you to brake, and the same for the car behind you, and so on. The resulting concertina effect causes everyone else to slow down — in economics this is called an externality.

Such externalities are one reason why markets are rarely perfect — including the markets for roadspace or for transportation by escalator. Lane hoppers impose a delay on the other road users, and very similarly, people who choose to walk on a congested escalator impose a delay on everyone else.

The problem for TfL and its users is that it is only in certain situations that it’s better for everyone to stand. Not only is the old stand on the right heuristic still perfectly fine outside the peak hours, things also change according to the height of the escalator. An earlier trial at Canary Wharf station, where the height of the escalator was just 10m, found that with everybody standing capacity was reduced by 10%. (The Holborn escalator has a height of 24m.)

Heuristic versus nudge

Replacing a century-old heuristic with a new one would be quite a challenge. But even a new heuristic wouldn’t help here: a rule of thumb couldn’t really capture the complexity.

Is there another way to guide people guided towards the behaviour that is right for the location, and for the situation? How can passengers in a hurry be prevented from mindlessly pursuing the old heuristic, or from following their counterproductive instincts that cause others (and indeed themselves) delay?

The approach used to control traffic flow on motorways is not really suitable. It depends on enforcement, and fining passengers for walking when they shouldn’t would surely meet with protest. Would just telling people help?

Simply advertising what you want people to do is easy and straightforward, but it’s unlikely to have much effect here. Imagine posters explaining the conditions when walking is allowed, and when standing is de rigueur. Regular passengers would ignore the signs because they already know what they say. Occasional travellers might be intrigued by them, but both would still need to judge the height of the escalator and the congestion level to know whether they should stand on the left or are allowed to walk. Nope, the old heuristic won’t be beaten by something like that.

A dynamic eye-catching Walk/Don’t Walk sign at the start of the escalator would require a bit of technology to control it, but it might be more effective. At least it gives a visual cue when it matters. Or maybe the original technology could be reused? A looped spoken announcement saying “Walk on the left”, or “Don’t walk on the left” according to the situation would probably become annoying very quickly, however. And in both cases it would still be tempting for anyone on the left hand side, seeing half a dozen empty steps ahead, to start walking again to close the gap, of course immediately followed by everyone behind.

Seeing the light

Perhaps road traffic can provide inspiration after all. Environmental cues can influence how we behave, and traffic engineers in Japan (and elsewhere) have used this to great effect. Grooves in the so-called Melody Road produce a well-known tune you drive over them at a particular speed. And while sound might not be a good choice to influence pedestrians on an escalator, light might be a better cue.

A mechanism developed by three sports scientists, Liang Huang, Jie Zhuang and Yanxin Zhang, offers intriguing possibilities. Using a system of running lights they were able to control a subject’s walking speed in order to analyse their gait. So imagine a strip of lights on either side of an escalator. If the lights move at the same speed as the steps, people would be nudged to stand. When the situation allows for it, the lights on the left hand side could be made to move at a faster pace, thus encouraging them to walk (and help distracted passengers keep out of the way of their hurried fellow travellers).

The tube network becomes ever busier. TfL will need to come up with ways to maximize throughput in the stations during peak times, and avoid having to temporarily close them for safety reasons when they become congested.

Literally nudging people on escalators would probably be a violation of safety regulations, but a metaphorical nudge might just make travellers see the light and let go of the old heuristic.

Originally published at on March 10, 2017.

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Accidental behavioural economist in search of wisdom. Uses insights from (behavioural) economics in organization development. On Twitter as @koenfucius

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