This is true.
Baltimore was one of the cities NCL took over and converted to buses. I believe there's a book, "Who made our streetcars go?" documenting this.
In 1974, with the country facing jam packed roads and an oil shortage, the mayors of both San Francisco and Los Angeles pointed out that NCL had taken over key streetcar routes in their cities (Key System in SF) and converted them to buses, contributing to the mess.
As mentioned, NCL converted streetcars to buses in Philadelphia.
Now, NCL was not the only reason streetcars lost favor, there were other reasons, too. Nor would I call it a "conspiracy", rather, it was a business decision by automotive makers to vertically integrate to sell more of their products.
None the less, the actions of NCL were not in the nation's long term interest. The LA and SF mayors testified in detail before Congress of the problems that resutled.
As to commuter trains, high taxes assessed on them while roads had no taxes certainly was a very significant factor. When commuter trains first got into difficulty, the NYT did a study of the issue and noted [the] very heavy burden; back then, the commuter lines serving New York City were paying about a billion dollars in property taxes (in today's dollars). That's quite a hefty sum, especially when the competition is paying zero. The NYT also found that local towns were not about to cede the railroads any tax relief.
***** Moderator's Note *****The more I think about it, the less sure I am that this is a valid comparison. Railroads, as private corporations, are expected to pay taxes: public roads are paid for by the taxpayers, and while they don't generate any tax revenue while idle, the vehicles that use them pay exorbitant taxes: everything from levies on fuel to excises to "sales and use" taxes (which are 5% of "Blue Book" value in my state).
IMHO, pointing to a lack of taxes on roads, (which are, as public property, exempt) isn't an effective argument at a macroeconomic level. Railroads faded from prominence because they are too efficient, i.e., because selling, fixing, fueling, and taxing automobiles and trucks is both easier and more profitable than convincing the public to suffer the indignity of sitting next to someone who likes a different kind of newspaper than you do or wears different clothes.
Despite the barriers placed on them, some commuter rail systems continue to do well: with the economy down, suburban car owners are realizing that all the "little" costs of owning a car add up to a _lot_ more than the cost of a rail pass.
FWIW. YMMV (No pun intended).
Bill Horne Moderator