Trains are so popular on the East Coast, they’re giving other modes of transportation a run for their money. Amtrak carries more riders between Boston and New York, for example, than all of the airlines combined. Yet, service on the Boston to D.C. route is far from world class. Amtrak bills its Acela train as “high speed,” but trains on the same route half a century ago made it from South Station to the nation’s capital in far less time. And there are few alternatives: Highways are crowded and airports are as congested as the rail lines. Meanwhile, the US population is expected to swell into “megaregions” by 2050, compounding transportation and commuting needs. What does the future hold for rail in the Northeast?