Following the 1918 IRT expansion into the modern "H" system that serves Manhattan's East and West sides separately with the 42nd Street Shuttle connecting them, the Flivvers ran primarily on the Seventh Avenue–180th St. Bronx Park Express.

[1][2][3] Originally, when various High-V groups were delivered and readied for service, many drew their motors from the Composite fleet.

They were given new motors, new trucks, and low voltage equipment with the AMUE braking system, which was fast becoming the industry standard.

However, in the original assumption that all cars would be High-V trailers, they had already ordered the older AMRE braking system for this group.

Rather unique to the IRT system, these cars became known as the Flivvers, named after the apparatus used to control the doors that resembled the windup device on old type automobiles to start their engines.

's from the early 1950s, in the event of severe wintry weather such as snowstorms, the personnel were directed to operate as many trains of Flivvers as possible.

In 1921, in company with the Low-Vs and Steinways, all Flivvers, being low voltage cars, were converted to MUDC practically in one fell swoop.