Forbes article on electrification especially in North America. Article says major cost is getting sufficient clearance for CAT. Maintains batteries solution for meeting tunnel and bridge clearances. However IMO most dead areas that have insuffient clearances are rather short rail distances. IMO operating trains with a top and tail of electric DPUs would solve most of these problems except for tunnels longer than most trains. Those trains yes would need battery carrying locos. Horse shoe route and maybe just a few others in the east. Out west some tunnels already have enough clearance . Follow link for more detail :