Michael Bloomberg, Mayor of New York, has said he always walks on escalators. Good exercise, yes, but some cities discourage it. And there's one thing obstructing walkers - people who stand.

There are walkers and there are standers, and Mayor Michael Bloomberg is a walker.

In announcing a plan to make New York's buildings more stair-friendly, the mayor said he always walks on escalators.

Most escalator walking happens at underground stations - people don't tend to be in such a hurry in a shopping centre, for instance.

But Bloomberg is still in a minority of escalator users around the world. In London, about 25% of people on the Tube walk on the escalators and in Shanghai only about 3%, according to a study.

And in some countries, walking on escalators is discouraged. On the Toronto subway system, signs that encouraged people to walk on the left were removed at the recommendation of safety experts.

Gripes - the big three Standing on wrong side

Luggage in walking lane

Stopping when disembarking

A ban was also considered for Tokyo's transport system but never enforced. And in the UK, people of a certain age will remember the chilling public information films of the 1970s that featured a pair of children's blue wellington boots getting sucked into the machinery. "Stand still and don't walk down," it urged.

Either that message never got through or it was soon forgotten, because any such caution has melted away in the UK. There are 426 escalators on the London Underground and there's a signposted system of standing to the right and walking to the left.

Research in 2011 by the University of Greenwich found that 75% of people at Paddington Tube station stood and the left-right rule was observed by nearly 90% of people.

But the custom varies depending where you are. The same team of researchers, led by Edwin Galea, earlier found that in Shanghai, only 2.4% walked and there was no preferred side to walk on.

Usually there is a walking lane on busy subway escalators, says Galea, and it's not clear if the Shanghai free-for-all reflected a cultural phenomenon or was simply people getting to grips with what was a new station and escalator.

Image caption Get stuck behind this lot and you've missed your train

Most escalators across the world that do have a standing/walking system follow the "walk on the left" custom, to speed up the flow. One of the exceptions is Australia, where people walk on the right.

It's interesting that so many countries walk left, says Galea, but no-one's quite sure why. "It could be a random effect, it could be a copy effect, or it could have something to do with the side of the road we drive on. It could be some kind of rationalisation based on this."

A walker's view "You're too tired to walk? Counterpoint: no, you're not. How did you get in this subway station to begin with? Were you hauled here in a wheelbarrow? How do you move about the city? Are you carried by the scruff of your neck in your mother's mouth like a wayward puppy? I suspect that, no, you walk. You walked here. You can walk down the escalator. All of us are tired, you see. That is why we don't want to spend any more time in this train station than is absolutely necessary. That is why we want to catch the first available train - the train that is about to pull in now. Which we will miss. Because we are stuck on this escalator." Hamilton Nolan, Gawker

The British drive on the left and so choose to walk that side on escalators, he says, but in countries that drive on the right, the rationale could be that you drive on the right so you stand on the right.

But one thing unites all the cities that do have a system - there's conflict when people obstruct the walking lane.

"Able-bodied people standing on the downward escalator are in effect robbing the people behind them of time," says Hamilton Nolan, who writes for Gawker and regularly uses the New York subway.

"Their presumptuous need for leisure may cause everyone behind them to miss a train they would have otherwise caught. Then those people are forced to stand and wait on a subway platform for many extra minutes. Those are precious minutes of life that none of us will get back."

It's not open war, he adds, it's a war waged in the privacy of the enraged minds of walkers who are forced to stand impatiently behind as the escalator slowly descends.

But people who stand defend themselves by telling walkers not to be so impatient, because the escalator is doing the work for them.

On one forum, a stander says: "If the person is in such a rush, why not just take the stairs? Even when the escalator is packed and there's nowhere to move, I see these same people moaning and groaning about not being able to pass."

There are plenty of examples online of frustrated commuters venting their anger about what they regard as anti-social behaviour. Pet gripes are people standing on the wrong side, not leaving enough space between standers, stopping at the top and blocking the way with luggage.

San Francisco artist Helen Tseng summed up the gripes in one illustration commissioned by a website called The Bold Italic.

Image caption Illustration by Helen Tseng for the Bold Italic website

Her picture, published in January, was widely picked up by other media and she thinks the subject tapped into something that people were unconsciously thinking - the etiquette of escalator travel. "Going on escalators is a universal thing, analogous to traffic, and people get traffic rage too."

In Toronto, that tension has been defused since the signs telling people to walk on the left were removed, says commuter Tom Robertson. "You can tell some people get a little annoyed when they are standing behind someone on the left but I've never seen anyone say anything about it. I think many people have forgotten about the signs."

A spokesman for the Toronto Transit Commission said he could not recall any escalator accidents in Toronto.

Indeed, injuries and fatalities on escalators are rare. In Beijing, one died and dozens were injured in 2011 when an escalator suddenly changed direction and threw them off balance. Other cases have involved people being entrapped by clothes or hair, but deaths are very rare.

Despite the blue wellingtons being chewed up in the film, the chance of a stray shoelace or skirt getting caught in the gap between moving steps is minimum, says David Chan of City University London, who researched safety as a consultant on a project to design a curved escalator.

But if you really want to avoid escalators, you should move to Wyoming.

The US state has only two escalators, both in a bank.