[18] The new trains will have greater passenger capacity and an enhanced active tilt system that will allow higher speed on the many curved sections of the route.

[19][20] Following the success of Japan's newly inaugurated Shinkansen network, the High Speed Ground Transportation Act of 1965 authorized the U.S. government to explore the creation of high-speed rail, which resulted in the introduction of the higher-speed Metroliner trains between Washington, D.C., and New York City in 1969, the predecessor to Acela.

An X 2000 train was leased from Sweden for test runs from October 1992 to January 1993, followed by revenue service between Washington, D.C., and New York City from February to May and August to September 1993.

[23] On March 9, 1999, Amtrak unveiled its plan for the Acela Express, a high-speed train on the Northeast Corridor between Washington, D.C., and Boston.

[29] Amtrak's original contract with the Bombardier-Alstom consortium was for the delivery of 20 trainsets (six coaches each, with power cars at front and rear) for $800 million.

[30] By 2004, Amtrak had settled contract disputes with the consortium, paying a total of $1.2 billion for the 20 trainsets plus 15 extra high-speed locomotives and the construction of maintenance facilities in Boston, New York, and Washington.

[39] In January 2014, Amtrak issued a request for proposals on 28 or more new model Acela trainsets, in a combined order with the California High-Speed Rail Authority.

[40] After discussions with manufacturers, Amtrak and the California High Speed Rail Authority concluded their needs were too disparate for common rolling stock and decided not to pursue the joint option.

[52] At the same time, Amtrak introduced the Acela Nonstop, a direct train from Washington, D.C., to New York's Penn Station.

[53] The first-generation Acela trainset is a unique set of vehicles designed specifically to satisfy governmental rolling stock requirements established primarily by the Federal Railroad Administration (FRA).

[32] The design, using identical 6,200 horsepower (4,600 kW) power cars at each end which operate on voltages of 12 kV, 12.5 kV, and 25 kV AC, and either 25 or 60 Hz frequency, derives several components from the TGV,[54] such as the third-generation TGV's traction system (including the four asynchronous AC motors per power car, rectifiers, inverters, and regenerative braking), the trucks/bogies structure (a long-wheelbase dual transom H frame welded steel with outboard mounted tapered roller bearings), the brake discs (although there are only three per axle, versus four on the TGV), and crash energy management techniques to control structural deformation in the event of an accident.

[55][54] The tilting carriages are based upon Bombardier's earlier LRC trains used on Via Rail rather than the TGV's non-tilting articulated trailers.

[54] The Tier II crash standards, adopted in 1999, have also resulted in the passenger cars being designed without steps and trapdoors, which means that the trainsets can only serve lines with high-level platforms such as the Northeast Corridor.

[59] On August 26, 2016, then-Vice President Joe Biden announced a $2.45 billion federal loan package to pay for new equipment for the Acela Express service, as well as upgrades to the NEC.

$450 million was allotted by President Barack Obama's administration to replace catenary and upgrade signals[65] between Trenton and New Brunswick, which will allow speeds of 160 mph (257 km/h) over a 23 mi (37 km) stretch.

[66] This section of track holds the record for the highest speed by a train in the US, which is 170.8 mph (274.9 km/h), achieved in a test run by the U.S./Canada-built UAC TurboTrain on December 20, 1967.

[37][67] North of New York City, Amtrak upgraded the track along the Connecticut shoreline east of New Haven to allow maximum speeds in excess of 110 mph (177 km/h), in preparation for the Acela launch.

[68] Although this area contains the fastest current operating speeds (150 mph (241 km/h)), it also has the slowest section of the NEC: between New Rochelle, New York, and New Haven, Connecticut.

This section is owned by Metro-North Railroad and the Connecticut Department of Transportation and is heavily used by commuter trains which limit the speed of the Acela.

[69] In 1992, ConnDOT began plans to upgrade the catenary system and replace outdated bridges on the New Haven Line to enable the Acela to run slightly faster.

[70][needs update] On July 9, 2007, Amtrak introduced a limited-stop round trip, with trains stopping only at Philadelphia between New York and Washington.

[71] The dense population of the northeastern United States makes the Northeast Corridor the most heavily traveled portion of the American passenger rail system.

[73] Tilting enables passengers to ride more comfortably on curved sections of track faster than would otherwise be possible, by leaning into the bend.

[75] Due to the high speed at which Acela trains bypass platforms of local stations, concerns have mounted in some communities over inadequate warnings and safeguards for passengers waiting for other trains, including that the two-foot wide yellow platform markings may not keep people at a safe distance.

[76][77] Suggestions include platform safety barriers, or use of different announcements for approaching Acela trains versus slower ones.

In October 2012, Acela service was cancelled immediately before, during, and after Hurricane Sandy,[83] which damaged the North River Tunnels causing lasting delays and reliability problems.

In March 2020, all Acela trips were suspended as part of a round of service reduction in response to the COVID-19 pandemic in the United States.

The Acela trainsets underwent minor refurbishments between mid-2009 and 2010 at Penn Coach Yard, next to 30th Street Station in Philadelphia, Pennsylvania.

[87] In May 2018, Amtrak announced a 14-month program to refresh the interiors of the Acela trainsets, including new seat cushions and covers, new aisle carpeting, and a deep clean.

[93] A limited number of Acela trains previously stopped at New Rochelle, New York; New London, Connecticut; and Trenton, New Jersey; service was eliminated in 2021, 2022 and 2023, respectively.