Don't count on loops to indicate trolley. Every rapid transit line ended in loops at one time.
Dudley-Sullivan, Bowdoin-Maverick, Codman Yd.-Eliot Sq. They had loops when there was
land for them. The High Speed Line was looped from the beginning though, I don't think there were
any single ended cars on the system when it was built. Convenience with trailer trains was
a main motive for early surface loops. After the trailers were gone, the loops survived because they were
useful of themselves.
LS