further increasing speeds on existing track. Today, tilting passenger trains are commonplace. Talgo's trains are used on some short and medium distance routes such as Amtrak Cascades from Eugene, Oregon, to Vancouver, British Columbia. In August 2016, the Department of Transportation approved the largest loan in the department's history, $2.45 billion to upgrade the passenger train service in the Northeast region. The $2.45 billion will be used to purchase 28 new train sets for the high-speed Acela train between Washington through Philadelphia, New York and into Boston. The money will also be used build new stations and platforms. The money will also be used to rehabilitate railroad tracks and upgrade four stations, including Washington's Union Station and Baltimore's Penn Station. As of 2014, U.S. railroad mileage has stabilized at approximately . High-speed rail As of 2022, the only operating high speed rail service in the United States is Amtrak's Acela, between Washington, DC, and Boston. It currently has a maximum speed of , and only in some sections between Boston and Providence, RI, soon to be after introduction of new Avelia Liberty trains, eventually to be upgraded to over some sections. The state of California is constructing its own HSR system, California High-Speed Rail, constructed to standards in some places. The first section in the Central Valley is due to open around 2027. Rolling stock reporting marks Every piece of railroad rolling stock operating in North American interchange service is required to carry a standardized set of reporting marks. The marks are made up of a two- to four-letter code identifying the owner of the equipment accompanied by an identification number and statistics on the equipment's capacity and tare (unloaded) weight. Marks whose codes end in X (such as TTGX) are used on equipment owned by entities that are not common carrier railroads themselves. Marks whose codes end in U are used on containers that are carried in intermodal transport, and marks whose codes end in Z are used on trailers that are carried in intermodal transport, per ISO standard 6346). Most freight cars carry automatic equipment identification RFID transponders. Typically, railroads operating in the United States reserve one- to four-digit identification numbers for powered equipment such as diesel locomotives and six-digit identification numbers for unpowered equipment. There is no hard and fast rule for how equipment is numbered; each railroad maintains its own numbering policy for its equipment. List