I came across an article by planning prof. Donald Shoup in UCLA Magazine (sorry no link or date) titled “Paradise Paved.” He explaines how he tried to track down the source of this tidbit he read in a book written by two Berkeley professors: “In the United States, the automobile consumes close to half of the land area of cities; in Los Angeles, the figure approaches two-thirds.” Turns out the tidbit was probably made up, but Shoup did find another interesting bit from an Australian researcher who writes:
Shoup notes that streets existed long before cars and that “the share of urban land devoted to streets may even have declined since cars arrived.” And now for the bigger picture: If you grabbed 100 people off the street and asked the how much of our nation has been developed, what do you think they’d say? This study (pdf) by Ed Glaeser and Matthew Kahn points out that only about 5 percent of America is developed (see p. 36).