It doesn't need to be a dense neighborhood, but one that give you all you need to live.

Some city designers chose to make areas that are businesses only and living only - about the worst you can do for bike- and walkability

I grew up in a small town of 10k, mostly single family housing on relatively small plots. At the time most people didn't have cars and even old women biked to the church (and old men to the pub). Those who did not use the bike could walk, it took longer but was still possible because the shops, services, hospital, schools and offices/factories were close by. Only those who worked or studied in nearby towns used cars or buses/trains. Because of this, I think the most important variable is the availability and affordability of cars. Everything else follows.

That's a good point. Over a few decades the availability of cars naturally destroys the usefulness of other modes of transportation unless there is active effort to prevent these effects. Once most people have a car, small local shops aren't really viable anymore, for example. Too many people drive to the more convenient big shop that is further away.

> Over a few decades the availability of cars naturally destroys the usefulness of other modes of transportation unless there is active effort to prevent these effects.

That is simply not true. The car isn't some inherently superior mode of transportation. People will use whatever infrastructure a city invests into most. If you build a city where all the infrastructure budget is spent on cars, then is it any surprise people will use their car to get everywhere?

Once you force people to use cars to get anywhere, then of course that kills local shops, but that didn't happen simply because of the availability of cars. It happened because the city stopped investing into any infrastructure that's not designed for the car.

On top of that, as everything gets rebuilt to be more convenient for cars, this makes it too inconvenient for walking or cycling, because now there's huge parking lots everywhere, the streets (or stroads) are widened for all the car traffic, crossing these streets is now dangerous because of all the traffic, walking or cycling anywhere is dangerous and miserable because of all the noise and pollution from all the car traffic, etc. Cars only really work with walking and biking when a very small portion of the population has and uses cars. If you make your city so that everyone can conveniently have a car, that becomes the only convenient way of getting around.

I live in the dutch city of Eindhoven and it's both convenient to have a car and convenient to ride a bicycle. This is possible as long as you invest as much in bicycle infrastructure as you do in car infrastructure.

When a road becomes too wide to cross by bicycle the city here either builds a wide bicycle tunnel or a suspended bicycle roundabout. Those types of infrastructure are expensive, but it's the kind of thing you get if you don't put all of the city's infrastructure budget into one mode of transportation.

What does a suspended bicycle roundabout look like? Have some pictures: https://imgur.com/a/08RJEsk

Here's the location: https://goo.gl/maps/pBTFJGr9sbVHZeDT6

Here's an example of a bicycle tunnel: https://goo.gl/maps/GzAvRCMi1BoxLXgdA

And here it is from the cyclist's perspective: https://goo.gl/maps/mzogX37mqRqrK1JY8

And we also have bicycle roundabouts with tunnels: https://goo.gl/maps/ui28SMbKbXjbvevr5

Did you accidentally cut a freeway through your city? Just build a bicycle bridge over it: https://goo.gl/maps/WqLgJdhsTsr5sufE9

Of course you do need to make sure that there are actually places worthwhile going to within a convenient cycling distance. Which involves building lots of multi-family housing at the edges of downtown. With shops located within those neighborhoods. Rather than huge suburbs with exclusively single-family homes requiring a car to even do grocery shopping.

Also known as a radical monopoly: https://en.wikipedia.org/wiki/Radical_monopoly

For some data sources, there's only city data available:

> Since the bicycle and car trip shares from travel surveys are mainly for cities, we used the mean of city-level values as the corresponding national trip share, because the derived values appear in line with national values from other sources

A common measure for this is called "population-weighted population density", which more or less tries to capture the average local density that each person experiences.