Meanwhile, the automobile and its friend the truck have cost the central city some of its industrial dominance. In ever greater numbers, factories are locating in the suburbs or in ``industrial parks'' removed from the city's political jurisdiction. The appeal of the suburb is particularly strong for heavy industry, which must move bulky objects along a lengthy assembly line and wants enough land area to do the entire job on one floor. To light industry, the economies of being on one floor are much slighter, but efficiency engineers usually believe in them, and manufacturers looking for ways to cut costs cannot be prevented from turning to efficiency engineers.

This movement of industry away from the central cities is not so catastrophically new as some prophets seem to believe. It is merely the latest example of the leapfrog growth which formed the pattern of virtually all American cities. The big factories which are relatively near the centers of our cities -- the rubber factories in Akron, Chrysler's Detroit plants, U. S. Steel's Pittsburgh works -- often began on these sites at a time when that was the edge of the city, yet close to transport (river), storage (piers) and power (river). The ``leapfrog'' was a phenomenon of the railroad and the steam turbine, and the time when the belts of residence surrounding the old factory area were not yet blighted.

The truck and the car gave the manufacturer a new degree of freedom in selecting his plant site. Until internal combustion became cheap, he had to be near a railroad siding and a trolley line or an existing large community of lower-class homes. The railroad siding is still important -- it is usually, though not always, true that long-haul shipment by rail is cheaper than trucking. But anybody who promises a substantial volume of business can get a railroad to run a short spur to his plant these days, and many businesses can live without the railroad. And there are now many millions of workers for whom the factory with the big parking lot, which can be reached by driving across or against the usual pattern of rush hour traffic and grille route bus lines, is actually more convenient than the walk-to factory.