PASSENGER TRAIN EQUIPMENT - All Aboard: The Complete North American Train Travel Guide - page 140

Amtrak's regional service trains running between Boston and Washington, D.C., are
hauled by these very powerful HHP-8 all-electric locomotives. Photo by Chao-Hwa Chen
The newest of the Amtrak locomotives are the all-electric
HHP-8s that run between Boston and Washington, D.C., along
the Northeast Corridor and pull the trains that Amtrak refers
to as their Regional Service. These trains don't run quite as fast
as the Acelas, and some of them make a few more stops. The
“HHP” stands for “high horse power,” and the “8” signifies that
each of these babies can produce as much as 8,000 horsepower—
that makes the HHP-8 one of the most powerful railroad loco-
motives in the world. There are 15 of these engines in the Amtrak
fleet, and they routinely run at speeds of up to 125 miles an hour.
These locomotives look a lot like the power units on the Acela
trains, but they have a cab for the engineer at each end of the
unit.
The predecessor to the HHP-8 is still seeing regular service
in the Northeast Corridor. Designated AEM-7, this older model