Step inside the sprawling factory in California where the largest fleet replacement in Amtrak’s 55-year history is coming together piece by piece.

By Gabe Castro-Root

Visuals by Ruth Fremson

Reporting from the Siemens Mobility plant in Sacramento

Feb. 13, 2026

In the sleepy, car-centric outer reaches of Sacramento, across the street from low-slung homes and behind an unassuming wooden fence, the next generation of American passenger rail is taking shape.

Workers zip around in golf carts at the 60-acre, 2,500-employee Siemens Mobility plant, a behemoth complex of cavernous warehouses and towering machinery that at peak production can turn out a train car every day. Over the last few months, amid the rows and rows of rail cars in various stages of production, the newest Amtrak trains have finally begun rolling onto the tracks.

Airo, Amtrak’s name for its new arrivals, is set to bring the railroad company out of the 1970s and ’80s, when much of its current equipment was built. While early missteps slowed production and added costs, Airo trains will soon replace a painfully outdated fleet that lacks many modern conveniences and has become increasingly difficult to maintain.

Airo trains aren’t high speed — with an upper limit of 125 miles per hour, they’re not any faster than those they’ll supplant. But the new rail cars feature sleek interiors, grab-and-go food options and accessible designs for people with disabilities. Passengers will start to see Airo trains this summer on the Cascades route, in the Pacific Northwest, followed by more than a dozen East Coast routes beginning next year, including the Northeast Regional, the Carolinian, the Pennsylvanian and the Vermonter.

Amtrak has ordered 83 Airo trains for a total of $8 billion, the largest fleet replacement since the company was founded in 1971. The trains will be built over the next several years at the Sacramento plant, which also makes light-rail and intercity trains for other customers, and at another factory in North Carolina.

“We’re jumping about 50 years into the future,” said Derek Maier, a senior director of Amtrak’s Airo program. “It’s a more open experience. It’s better lit. It’s newer materials.”

When I visited the Sacramento plant with the photographer Ruth Fremson late last year, the first Airo train had been sent off for testing and the second was nearing completion.

Each train includes more than 3,500 parts manufactured by nearly 100 suppliers across 31 states. Assembling each one is like solving a supersize puzzle.

The process begins in the harness room, where the train’s wiring — more than 30 miles of it in each passenger car — is labeled, cut and connected. It’s then laid out and checked by hand to ensure each wire will be properly attached and secured in the train. About 140 technicians work here across three daily shifts.

Switch cabinets, which house the train’s electrical controls, are also built here.

In another building nearby, metalworkers weld the carbon steel frame of the train’s locomotive.

Passenger cars, made of stainless steel, are built in an area called the coach weld. Automated machinery performs 30,000 spot welds per car.

Ruth and I, along with our tour guides, wore safety vests, hard hats and goggles throughout our visit. We added ear protection in the welding areas, where loud noise is a regular part of the job.

The train’s wheels — and the gears, wires, brakes and springs that support them — come together in the bogie assembly. A bogie is essentially one unit of all those parts. A coach car’s bogie wheelset weighs more than 4,200 pounds, and a locomotive bogie wheelset weighs more than 7,200.

Airo’s 4,200-horsepower locomotive brings a long-anticipated feature to the rails: Unlike earlier models, it can change from diesel to electric at the flip of a switch, and some variants can even run on battery power. These capabilities will lower emissions and save time for travelers passing through Washington, D.C., where trains going between the electrified Northeast Corridor and the non-electrified network to the south must currently wait to switch locomotives.