Transportation systems acquired after 1950
All service performed in the employ of a State or political subdivision thereof in connection with its operation of a public transportation system shall constitute covered transportation service if the transportation system was not operated by the State or political subdivision prior to 1951 and, at the time of its first acquisition (after 1950) from private ownership of any part of its transportation system, the State or political subdivision did not have a general retirement system covering substantially all service performed in connection with the operation of the transportation system.