Perhaps there is a different term for the type of city you are thinking of, generally cities such as Letchworth[1] are moreso what is known as a garden city.
Historically, cities like Brasilia were designed around the logic of the car. For example, most roadway intersections feature over and underpasses, cars are completely segregated from pedestrians. By most accounts, it doesn't work so well.
But yeah, this kind of design doesn't seem to work well no matter the density of the buildings. Cities really need to work around pedestrians.