Had its origins in 1935 in Danville IL, when the brothers Dominick and Peter Giacoma began operating the Bee Line Transit Corp. south of Danville to Georgetown, replacing an Illinois Traction Co. interurban railway branch. The Giacoma brothers subsequently acquired additional bus companies in Midwest and southern states, and in 1951 incorporated American Transit Corp. (ATC) as a holding company for these bus companies. In 1966, ATC became a subsidiary of Chromalloy American Corp., a diversified conglomerate. And as more transit systems became publicly owned, ATC evolved to a management company for such transit systems. In 1987, Chromalloy American Corp. was acquired by Sun Chemical Corp., which manufactured printing ink. And in 1987, Sun Chemical Corp. changed its name to Sequa Corporation. And in 1989 Sequa sold ATC to Vancom, a family owned Chicago area school bus company which had been formed in 1925 and for many years was known as Van Der Aa Bus Lines. The school bus operations were sold in 1997 to Laidlaw, while the transit management company was sold in 2000 to National Express, operating intercity buses in Great Britain. And in 2005 ATC was sold to the France based company Connex, part of a diversified company which that same year adopted the name Veolia for all of its businesses. In 2011, Veolia acquired the France based transportation company Transdev, and in 2014 the name Transdev was adopted for the North American transit operations..


According to the 1952 "Mass Transportation's Directory", the following bus companies were associated with the name Giacoma. Data presumably is from shortly before ATC was formed.

By 1955, ATC had disposed of the Cairo and Dyersburg operations, and had added the following bus companies.

And following companies were added in subsequent years, up to the 1966 Chromalloy acquisition.

In 1960, the Shoals Transit and Suburban Transit operations were disposed of. Records are not clear after the 1966 Chromalloy acquisition. But by the mid 1970's, ATC still owned Bee Line Transit, which in 1964 acquired from National City Lines the Danville City Lines city operation. ATC also owned the Chicago & Calumet District Transit, the La Salle-Peru, and the Cape Girardeau operations. And ATC had begun managing publicly owned systems, some of which they formerly owned, and some additional systems.