Passenger car technology can be divided into “tilt” and “not-tilt” designs. Tilt equipment
differs from conventional, or “non-tilt,” car designs in that onboard hydraulic systems (active
tilt) or car suspension designs (passive tilt) smooth out curves to lower the centrifugal forces felt
inside cars. This in turn allows for the trains to operate at higher curve speeds, reducing overall
transit times. Applications include the Acela/American Flyer design, with an active tilting system
and commercial speeds of 150+ mph. The Acela system is currently in domestic use, while the
American Flyer is being tested.