The Comet IB cars were rebuilt from 30 former Penn Central Arrow I EMU cars originally built by the St. Louis Car Company between 1968 and 1969. The Arrow I cars suffered from chronic mechanical problems and were out of service by 1980. The cars sat unused for several years, but realizing that the car bodies still had many decades of service left on them, NJ Transit made the decision to have them rebuilt into un-powered coaches. In 1987 and 1988 the cars were converted into cab control cars and trailer coaches by Morrison-Knudsen for use on non-electrified lines. After two decades of service the Comet IB cars were retired by NJ Transit in late 2008, with some surplus cars temporarily leased to Exo's predecessor agency, the Agence métropolitaine de transport (AMT).