North-East Corridor (NEC)
The North-East Corridor (NEC) is a section of rail running from Boston to Washington, DC. Unlike most of the rest of the country, Amtrak itself owns and operates the tracks in the NEC. The NEC is electrified, and is home to the fastest trains in the country, such as the Acela.
Besides Amtrak, quite a few other regional railroads use parts of the NEC track.