The question is, where in NYC are you departing from, and where in the DC area are you heading?
As much as I love flying, on the east coast of the U.S. the train is the better bet for a couple of reasons:
#1 - Midtown Manhattan to downtown Washington DC. No long commutes to the airport - both train stations are tied into the cities' respective subway systems.
#2 - No security lines like the airports.
#3 - Extra room. No one is cramped on the train - wide and spacious, even at the cheapest level.
#4 - It is not terribly expensive to upgrade. First class and Acela cost more, but by comparison to F class on airplanes? No comparison.
#5 - Get up and move around. Enjoy the scenery. Let someone else deal with the hassles.
#6 - Scheduling. There are lots of trains, 24/7/365, and at all hours. Some leave NYC at 4:30 AM
arriving in DC 3½ hours later.
#7 - MOST of the time, traffic is not an issue. Airports get clogged, and traffic in the United States is reaching farcical levels. Delays happen on trains, but generally, they run on time.
Flying should be for longer distances - it's just too convenient to use Amtrak on certain routes.
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