excesses of some railroads and their owners, Congress created the Interstate Commerce Commission (ICC) in 1887. The ICC indirectly controlled the business activities of the railroads through issuance of extensive regulations. Congress also enacted antitrust legislation to prevent railroad monopolies, beginning with the Sherman Antitrust Act in 1890. 1901–1970 The principal mainline railroads concentrated their efforts on moving freight and passengers over long distances. But many had suburban services near large cities, which might also be served by Streetcar and Interurban lines. The Interurban was a concept which relied almost exclusively on passenger traffic for revenue. Unable to survive the Great Depression, the failure of most Interurbans by that time left many cities without suburban passenger railroads, although the largest cities such as New York City, Chicago, Boston and Philadelphia continued to have suburban service. The major railroads passenger flagship services included multi-day journeys on luxury trains resembling hotels, which were unable to compete with airlines in the 1950s. Rural communities were served by slow trains no more than twice a day. They survived until the 1960s because the same train hauled the Railway Post Office cars, paid for by the US Post Office. RPOs were withdrawn when mail sorting was mechanized. As early as the 1930s, automobile travel had begun to cut into the rail passenger market, somewhat reducing economies of scale, but it was the development of the Interstate Highway System and of commercial aviation in the 1950s and 1960s, as well as increasingly restrictive regulation, that dealt the most damaging blows to rail transportation, both passenger and freight. General Motors and others were convicted of running the streetcar industry into the ground purposefully in what is referred to as the Great American Streetcar Scandal. There was little point in operating passenger trains to advertise freight service when those who made decisions about freight shipping traveled by car and by air, and when the railroads' chief competitors for that market were interstate trucking companies. Soon, the only things keeping most passenger trains running were legal obligations. Meanwhile, companies who were interested in using railroads for profitable freight traffic were looking for ways to get out of those legal obligations, and it looked like intercity passenger rail service would soon become extinct in the United States beyond a few highly populated corridors. The final blow for passenger trains in the U.S. came with the loss of railroad post offices