I think it was both . Remember, people were still terrified of aerial bombing and the idea that an enemy by acquire the Bomb.
That may indeed be the case and I was really speaking from my knowledge of the town I grew up in. In upstate NY, many smaller, less urban locales are located along waterways and that probably provided an advantage to manufacturing - they could locate in many places so long as it was on the water and still get goods to market (and the Eerie Canalway opened up huge amounts of land to this possibility). But where I grew up, the only industry int he area was a paper mill and they did not employ large numbers of people. I would say, though, that short of being along a waterway, access to a highway for suburban areas would seem to be a boon for both commuting and locating manufacturing (making it possible) as it facilitates getting goods to market. In the case of Philly, all the port activity happens in the city. In the early farming days, my home town provided milled wheat to New Jersey and New York state by accessing an area of the Delaware River south of Philly but for whatever reason there never emerged an industrial base there. Still almost everything went to the ports in Philly before being redistributed regionally. The pattern I mentioned is also echoed by Dolores Hayden's book on suburbia but you are right in that it was more complicated than I presented and there really was no one reason for or pattern of suburbanization, especially in those early years.In the 1950s, President Dwight D. Eisenhower saw the need for the United States to have sufficient evacuation routes for both military vehicles and private citizens in the event of a war with the Soviet Union.



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..........You're also arguing that running trains in a single direction at capacity and over an equivalent number of track miles would be less efficient than running cars over freeways the same way. So, high-speed trains with their high-capacity throughput are less efficient than cars?
riiiight. When Pigs fly and the republicans in the state house/assembly vote for gay marriage will the high speed rail ever turn a profit.