Most of the US freight rail system isn't electrified because the capital expenditures of doing so would be very large, and its return on investment in terms of direct monetary savings wouldn't materialize for many, many years. Since externalities aren't priced in, diesel-electric locomotives haul most trains in the US. More passenger rail isn't really being built in the US, because the capital expenditures of doing s…
So far as adding more passenger rail lines, it isn't easy. For instance, plans for HSR in California are unrealistic because you don't save any time from SF to LA unless you can go from downtown to downtown. Sure you can build track in the Central Valley, but it would be pretty hard to take enough land by eminent domain to build a track into the cities even if these people were not the most feared NIMBYs on the planet.