Silver Line to Logan bus: why?

Question

does it stop to switch to diesel power, before it goes on the last stretch to the airport?

Answer 1

Because it's the (T). You are not expecting something designed intelligently are you? They had the opportunity to do it right (electric light-rail) but decided instead to implement a halfway thought out version of "Bus Rapid Transit". Lack of overhead catenary is the "reason" but that reason is also a sad and poor excuse.

Answer 2

Well, there are no overhead lines in which it draws electricity from once it leaves Silver Line Way.