> this policy might not translate to the real world as intended.

Certainly there's no guarantees but it's not as if there is a lack of good examples of success of mixed-use zoning. NYC is a common example in the US but there's similar ones all over the world.

> More people will invariably mean more cars.

If you worked ~ten blocks away from where you lived, would you get in a car to get there (knowing that it would take about the same overall duration or longer via car)? Seems especially nice that you could count on favorable weather most of the time.