It probably took someone from outside to point out the obvious

Perhaps you were listening to NPR yesterday and you noticed that Jane Jacobs died. The Times has a nice obituary, which is fitting, because New York City perhaps owes more than any other city (except possibly Toronto) to her personal efforts. If you're not familiar with her, Ms. Jacobs was almost certainly the most controversial figure in urban planning in the 20th century. She challenged many of the sacred cows which had developed in the first half of the century, such as the ideal of the Garden City (i.e. Le Corbusier) and the importance of zoning (she demonstrated rather effectively, I think, that zoning is simply the wrong way to go about urban planning; too bad even urban planners who know her work backwards and forwards all too frequently ignore that advice).

Her four part formula for a successful and diverse city block is so simple, but so nearly impossible to pull off (1. A street or district must serve several primary functions. 2. Blocks must be short. 3. Buildings must vary in age, condition, use and rentals. 4. Population must be dense.). Numbers 1 and 3 seem to be the hardest ones to fulfill these days, although I'd say we're getting better with number 1, at least in some municipalities (the Rosslyn-Clarendon-Ballston corridor in Arlington, for example). Number 3, though, is virtually impossible to fulfill in today's building world, where developers tear down entire city blocks to erect new buildings. The problem, of course, is that its just not efficient to slowly renovate blocks building by building on a city wide scale. I definitely think the importance of #3 is what the new urbanists have missed (although it probably isn't so much that they missed it as that they couldn't think of a way to convince any sane [read: money-loving] developer to implement it).

As a side note, I find it funny that she was considered so liberal (she certainly considered herself liberal), as many of her ideas were simply negations of previous liberal ideas.