E-PTL-4 is used east of the Newton (I-95) tolls, including the tunnels and I-93 in Boston. Troop E patrols not only the Turnpike, but I-93 within the area of the Big Dig. Which makes things a bit confusing at times as Troop H patrols the parts of I-93 outside of the Big Dig areas.
E-PTL-1 is used west of I-95, at least as far as the Sturbridge area. There is still activity on the high band system and the two are not patched together.
Gary