In 1946 E. Quinby alerted transportation officials across the county to what he called "A careful, deliberately planned campaign to swindle you out of your most important and valuable public utilities, your Electric Railway System". General Motors and others were subsequently convicted in 1949 of conspiring to monopolize the sale of buses and related products via a complex network of linked holding companies including National City Lines and Pacific City Lines. They were also indicted, but acquitted of conspiring to monopolize the ownership of these companies. In the period from 1936 and 1950 they had been involved in the conversion of over 100 electric surface-traction systems that were converted to bus systems in 45 cities including Baltimore, Los Angeles (mainly the "Yellow Cars"), New York City, Oakland and San Diego.

In the 1970s at around the time of the 1973 oil crisis controversial new testimony was presented to a United States Senate inquiry into the causes of the decline of transit car systems in the USA. This alleged that there was a wider conspiracy, by General Motors in particular, to destroy effective public transport systems in order to increase sales of automobiles and that this was implemented with great effect to the detriment of many cities.

Today it is agreed that General Motors and others were indeed actively involved in an largely unpublicized program to buy up many streetcar systems and convert them to use buses, which they often supplied. There is also acknowledgment that the Great Depression, the Public Utility Holding Company Act of 1935, labor unrest, market forces, rapidly increasing traffic congestion, taxation policies that favored private vehicle ownership, urban sprawl, and general enthusiasm for the automobile played a major or possibly more significant role."