Acela Express is the first service that could be considered
a high-speed passenger rail line. At the time I took it in 2014, the service
ran on the Northeast Corridor between Boston and Washington, DC with 14 intermediate stops.
The service attained peak speed of 150 MPH on short stretches of track
in Massachusetts and Rhode Island, but average speeds over the entire
line were in the 65-80 MPH range. Being only marginally faster than
conventional NEC service, the service can probably more appropriately
be seen as a premium service that features aesthetically-pleasing
rolling stock, higher fares, and a more elite clientele.
The service debuted in 2000 and has been a strong revenue
generator for Amtrak - although the opacity of Amtrak's accounting
procedures makes this subject to debate.