A completed Amtrak Acela trainset in the yard at the Alstom production facility in Hornell, N.Y., last summer. Heather Ainsworth/The Washington Post

Amtrak’s plan to roll out higher-speed trains in the Northeast Corridor this year has been derailed amid complications in completing testing of the new train sets along the route’s decrepit infrastructure.

New Acela trains scheduled to debut this fall need more analysis to ensure they can safely operate on the curvy and aging tracks between Washington and Boston, railroad officials said, saying the new trains are now slated to enter service in 2024, at least three years behind schedule.

The 28 Avelia Liberty high-speed trains, which will replace Amtrak’s existing Acela fleet, are part of a $2.5 billion investment supporting upgrades to passenger service through the nation’s busiest rail stations. The trains will come with improved safety, reliability, rider comfort and capacity, railroad officials said.

But their delivery has been snarled by multiple delays, including some stemming from unforeseen complexities in testing and computer simulation processes required by the Federal Railroad Administration. Amtrak and train manufacturer Alstom have cited some compatibility hiccups between the high-tech train, modeled after those in operation across Europe, and infrastructure that dates back 190 years in some areas.

The latest hurdle, officials said, involves testing the train’s wheels, particularly at higher speeds.

“The modeling of the wheel-to-track interface is particularly complex due to age, condition, and specific characteristics of Amtrak infrastructure on the Northeast corridor, and especially the existing tracks,” Alstom said in a statement.

The company said it has been “conducting extensive investigations” to ensure trains will operate safely in all conditions. It added: “We are confident that this extensive process will demonstrate the compatibility of the latest generation of high-speed technology with existing [Amtrak] infrastructure.”

Alstom workers install underframe fairings to an Amtrak Acela train at the Alstom production facility in Hornell, N.Y. Heather Ainsworth/The Washington Post

Amtrak last year pushed the debut of the trains by 18 months from spring 2022 to fall 2023, citing the need for more testing because of the train’s construction with adjoining coaches sharing a single wheel assembly. The articulated train, a structure that minimizes bouncing felt by passengers and that improves the quality of the ride, proved to be more challenging from a testing perspective, officials said at the time.

Design changes in recent years have helped to address incompatibility with the corridor’s catenary system – the overhead wires that supply the train with electricity. The trains had to be modified after a prototype train that began tests on the route in 2020 lost contact with the electrified wire and could not reach optimal speed. Officials said adjustments were made to ensure the device atop the train that makes contact with the wire will perform properly.

Amtrak this past week said “further refinement of analysis, simulations and testing” is needed, which will mean delays in the delivery of the trains to Amtrak. Alstom said it has shipped six trains to the railroad and is preparing to deliver the seventh while it continues to make progress on the remaining 21 train sets.

“We want our customers to experience these new trains as soon as possible, but Amtrak cannot operate them for passenger service until Alstom has completed testing and meets all safety requirements,” Amtrak said in a statement.

Alstom and Amtrak have also cited challenges caused by the pandemic, including supply chain issues, as contributing to delays. They also noted these are the first train sets built under an FRA rule that establishes new safety standards for high-speed trains.

Amtrak in the coming months will seek approval from the FRA to operate on Northeast Corridor tracks, as well as for passenger safety standards and emergency preparedness requirements.

A required towing training was successfully tested in recent days between Philadelphia and New York with federal inspectors aboard, said FRA spokesman Warren Flatau. He said the agency expects Amtrak will submit the results of December testing on sections of the corridor and a simulation testing plan next month. Approvals would lead to another round of testing requirements.

Alstom’s $1.8 billion contract with Amtrak includes 28 train sets as well as 15 years of technical support and maintenance. The trains are being assembled at Alstom’s plant in Hornell, N.Y.

Amtrak’s inspector general in 2020 warned that any hiccups in the delivery of the trains would result in delaying the upgrade, costing Amtrak millions of dollars in potential revenue. Demand for Acela, a service used primarily by business travelers, was severely affected by the pandemic, but Amtrak officials have said ridership is bouncing back.

The new trains for Amtrak’s premier service will travel at top speeds of 160 mph, outrunning legacy Acelas that travel up to 150 mph – the nation’s fastest passenger train. The trains will accommodate up to 386 passengers, an increase of 25%, according to Amtrak.