IT has long been recognized that 20th-century suburbanization and “urban sprawl” have been made possible by near-universal automobile ownership and the availability of inexpensive gasoline. Consequently, the recent shortages and sharply rising prices of gasoline, and forecasts of the end of the era of abundant cheap petroleum, have prompted some speculation that the mobility of Americans will be constrained and the long trend toward the suburbanization of America will be halted.