A Trolley is a vehicle in Infamous 2 that replaces the Train in the first game. The trolley travels around all districts of New Marais except Flood Town. The trolley differs from the train in many ways. First of all, it travels at ground level instead of at an elevated platform.
Second, the trolley actually stops when you're in front of it unlike the train, which can run you over, so the trolley doesn't kill or damage you. One similarity they do share is that they cannot be destroyed by any means, with the only exception being in the mission "BOOM!".