It has been the same in east Asia (everywhere) for most of my lifetime. People walk more and stay slimmer and more healthy. Today in Taiwan there is much use of motor scooters or motorcycles (which are ubiquitous) and considerable use of cars, even for short trips, so many young people now are flabby and obese.

The neighborhood I live in in a United States outer-ring suburb has a city trail system. We use the trail to walk to the library (about a 2.6 mile round trip), shopping (similar distance in a slightly different direction), and to soccer practices (a bit farther). We don't like to burn gasoline, and use a handcart to move groceries on foot.

There is a negative feedback loop in crowded cities. It is polluted outside so walking is actually bad for your health, and then, you want to spend as little time as possible outside so you use whatever is fastest.

Thought experiment: suppose you are dictator, what would you do?

I might first propose a walk-only zones in certain times of week (a la hokousha tengoku).

I'd like to see a study exploring the net health effect of exercising outside in a polluted city.

Also, if it's polluted outside, isn't it polluted inside too? Do these cities all have buildings with air purifiers?

Physically I would say yes (air purifiers). Central AC that is. Not sure the efficacy.

Also, particulate matter is much more volatile outdoors, because it's outdoors.

And, the downmods, two in a row, make zero sense. Else, explain it please.

We do have walk-only zones in most inner-cities in Germany. They are called Fußgängerzonen (pedestrian areas). They are usually the main shopping avenues.

I am surprised that something as everyday as these gets suggested as an outlandish experiment. ;o)

Were I the dictator, I'd just narrow the roads to one lane plus on-street parking and replace the freed area with trees or bushes (or tram tracks). Narrowing forces cars to slow down, making pedestrians safer and allowing bicyclists better blend with the traffic. Cutting down on the lanes adds congestion which effectively removes unnecessary car travel from the city area, encouraging people to walk or pedal. I would also remove huge parking lots as they alienate pedestrians and increase car travel. Certain downtown streets or blocks could be made pedestrian-only zones.

Wouldn't this affect business travel, such as deliveries to restaurants, offices, grocery stores, etc.? I think the primary thing to cut down on is luxury travel, where walking/cycling/public transit it a reasonable alternative - and to do it without hindering business.

I don't know that it would really (it doesn't in Japan), but it seemed like a potential catch.