Start of the bullet train service between Guangzhou and Beijing, China, is the longest train line of its kind in the world. Using magnetic levitation to reduce friction between the track and cars, the train will zoom along at 186 miles per hour. If a similar train were built between New York and Washington, DC, then it would take a mere 72 minutes to complete the 226 miles.
Amtrak trains hobble along the Acela corridor at an average speed of about 71 MPH, even though they're capable of reaching speeds up to 150 MPH. The reason they travel so slowly lies in the train tracks themselves. The route between Boston and DC is such that trains have to constantly slow down in order to bank a curve or negotiate a hilly climb. Laying down straighter track would require a massive amount of labor and materials, which is why some politicians think the private rail industry should intervene. At the moment, high speed rail isn't coming to New York, or elsewhere on the Acela line.