After taking delivery of the 38 Silverliner cars, the PRR took the Pioneer III cars off intercity operations and used them exclusively on Philadelphia-area commuter service. In 1967, when SEPTA and the PRR took delivery of a second "Silverliner" MU car order from the St. Louis Car Company, the first (1963) "Silverliner" delivery became the "Silverliner II" cars and the 1967 order, the "Silverliner III." Although still officially called the Pioneer III, these cars were retroactively given the "Silverliner I" designation. As part of the Penn Central merger, the cars were also renumbered, out of sequence, to 294–299. By that time, the three disc-braked cars, together with all of the PRR Silverliner IIs, had been retrofitted with tread brakes, with which the Silverliner IIIs came equipped.