I do not buy that all. They say that streetcars were on their way out anyway because buses were more efficient. There is a significant hole in this reasoning because:
(a) GM is not in the business of owning street car lines;
(b) GM spent considerable money to buy out the street car lines, nevertheless.
If the street car lines were on their way out anyways why did GM spend so much money on something very much out of their usual line business? It may not be true that GM was the sole reason streetcars went away there may have been other factors, but it is hard to deny that GM played a role and a very significant role as they were the party that did the actual physical destruction.
And, by the way, the only reason buses seemed cheaper at the time was subsidies. Street cars had to pay for the building and upkeep of their rails, while buses used the streets, and the city paid for upkeep of the streets. One usually does not consider the damage buses do on the streets, but it is pretty significant because heavy vehicles do disproportionate amount of damage to asphalt. When all costs are added up, light rail is usually much more efficient than buses and that is before you even consider environmental costs.
It is quite possible that as citizens started worrying over their tax bills they would require bus companies to pay for the use of city streets. Interstate truckers, for example, are taxed for use of the highways. In that case, street cars would again become cheaper to operate than buses.