Grade crossings are fine for passenger multiple units (have pickup shoes at both ends of the train and a gap either side of the crossing) but not great for loco

Grade crossings are fine for passenger multiple units (have pickup shoes at both ends of the train and a gap either side of the crossing) but not great for locomotives. The other big problem (in addition to the ones you've outlined) is that having miles of live conductor at ground level isn't particularly safe - for track crew, trespassers, or wildlife. Britain has essentially stopped installing third rail for all these reasons. It's all 25kV overhead now.