I notice that dwg has a November '67 rev date on it, It needs to be remembered that prior to the Metroliners, the inside pair of tracks were used for through freight trains, and up until that date there were still a lot of them. Freights via the low grade Phily bypass came on and off just across the river at Morrisville, while frts going up the Bel-Del to bypass New York were also significant prior to the Penn Central merger. It looks to me like the limited distance between the east end of the platforms and the Bel-Del branch at the upper right is what determined the need for slips here, especially to get a nb Bel-Del across the wb psgr tracks after a wb psgr had arrived. It's interesting to note that the two "passenger mains" did not have slips.
Best rgds, SZ
