Link: https://en.wikipedia.org/wiki/Amtrak_Airo

Amtrak Airo is a new class of intercity, high-speed passenger trainsets being built by Siemens Mobility for Amtrak. The trainsets are based on the Siemens Charger ALC-42E locomotives and Siemens Venture passenger cars, and are intended to replace older equipment used on the Northeast Corridor and state-supported routes throughout the United States.

Service is expected to start on the Cascades in late 2026. Service on the Northeast Regional is expected in 2027, and on the Carolinian, Downeaster, Keystone, Palmetto, Pennsylvanian, and Vermonter in 2029. Service is expected to start in 2030 on the Adirondack, Empire Service, Ethan Allen Express, and Maple Leaf.

Most Amtrak Airo trainsets are designed to operate on both electrified and non-electrified lines without the need to change locomotives. This is achieved through a hybrid configuration using a Siemens Charger ALC-42E diesel-electric locomotive and either an Auxiliary Power Vehicle (APV) or a battery car.

The APV will be used on trains that use track with overhead lines (catenary).

Has it happened? I know they're testing on the cascades but haven't seen anything for a full start date

More diesel, boo.

(I kid. Trains are always an improvement over cars and aircraft, but man this country needs to fully electrify already.)

Until the freight railroads that host most passenger trains can be convinced that electrification is good for them -- and it definitely would be, looking at every other electrified mainline railway in the world is -- it sadly won't happen anytime soon under private ownership.

As an example, UP has been unusually hostile to overhead wires, claiming that they limit the vertical loading gauge to prevent double stacked containers. This is one reason why the farther part of the Caltrain service from San Francisco remains unelectrified, even after the publicly-owned rail section was successfully electrified to San Jose in 2024. Union Pacific refused to allow wires over their tracks down to Gilroy. This is an oddity for UP because they inherited the Southern Pacific's freight trackage rights on Caltrain's tracks, and do use those rights to service industrial customers on the way to San Francisco; I find their overhead wire argument to be unconvincing since if true, means that they're chosen to give up any possibility of serving these industrial customers with double stack consists forever after 2024.

The obvious locations would be steep, single track sections of the transcontinental lines through in the Western USA, where electric locomotives would have a pronounced climbing speed advantage that increases track capacity without having to build a second track.

Diesel electric locomotives are somewhere on the order of 100 times the efficiency of tractor trailers, which are themselves much more efficient than cars per ton-mile. If all road transit was replaced by diesel electric trains it would cut transit emissions to almost nothing. That of course would still only eliminate a fraction of total emissions, since most emissions are not transit-based.