All trolley means is that they get their power from an overhead wire. Heavy rail need not even be electric. Union Pacific and BNSF freight trains are heavy rail. The Silverliner V cars used in Denver's commuter lines came out from Philadelphia pulled dead-in-consist in freight trains. In contrast Denver's light rail vehicles,Siemens SD-100s and SD-160s, were brought out from Sacramento on flat cars because their frames could not withstand the stresses of rolling along coupled into a freight train.