More Density for Bigger Cities

I recently have noticed lots of comments in blogs and listservs on ideal densities.  But the ideal density for a city or a neighborhood (if there is such a thing) depends on context.

'

Why?  The smaller the city, the less density you need for walkability.  In a city with 20,000 people, 20,000 people per square mile (roughly equivalent to a gross density of 15 units per acre, assuming two persons per household) means a one square mile city- an extremely walkable small town.

But in a region with 20 million people, 20,000/square mile means that these people are spread out over 1000 square miles (the size of Long Island), the kind of geographic expanse that leads to really long commutes even if lots of people have good transit. In other words, this density level just gives us dense sprawl (and we've seen how well that worked for Los Angeles!) . This problem is, I think, one reason why LA, with only 30 percent less central-city density than Washington or Chicago, is far more than 30 percent more car-oriented than those cities.

Thus, a high density for a small city would still be too low for a big city to be anything but Traffic Hell.