One of the major moves David Gunn made, while he was head of SEPTA back in the late '70s and early '80s, was the curtailment of its regional rail lines back into electrified territory, a move rail advocates have regretted ever since. The stated reason was that the new Center City Commuter Connection wouldn't allow scheduled diesel service, implicitly that the Reading Terminal was going to be closed down. But the problem is that this was a red herring: SEPTA's planners could have, with some clever easement tricks, retained diesel services into 30th Street or Suburban Stations. Below is one way I penciled out how.
--The counter to this, though, is that the vehicles providing this service, Budd RDCs, were ending their design life at the time*, and their replacement, the SPV-2000, was so atrociously bad only the really clueless agencies ever ordered them.
--Countering that counter one would note that this was the era of the Comet I and the F40PH; again, had service retention been paramount, there would have been a way. But of course, all the political will of the era was focused on the tunnel, which leaves to us the task of picking up the pieces.