Audrey Henderson, 2017, Public Transit and the Benefits of High-Speed Rail, https://www.smartcitiesdive.com/ex/sustainablecitiescollective/benefits-high-speed-rail/151136/
The definition for high-speed rail in the United States differs from the definition used in the rest of the world, where high-speed rail is faster. For instance, the definition of high-speed rail in the European Union covers trains that travel up to 250 km/h (or 156 mph) on newly constructed lines. The EU defines high-speed rail on converted or upgraded lines as trains that travel up to 220 km/h (or 136 mph). At this writing, only one rail line in the United States meets the EU standard for high-speed rail: the Acela Express, an Amtrak train that runs Between Boston, New York City, Philadelphia, Baltimore and Washington, D.C. The Acela Express averages 68 mph (or 109 km/h) for its entire distance, but reaches 150 mph (or 240 km/h) for brief stretches of its run.
By contrast, the United States has designated three categories of high-speed rail: Emerging, Regional and Express. Emerging high-speed rail covers corridors ranging from 100 to 500 miles in distance (or 160 to 800 kilometers) long that have potential for supporting future high-speed rail development for trains traveling between 90 to 110 mph (or 145 to 177 km/h) on shared track. Regional high-speed rail is defined as service between population centers located between 100 and 500 miles apart (or 160 to 800 kilometers), and trains with top speeds ranging from 110 to 150 mph (or 177 to 240 km/h) with some dedicated track and some shared track. Express high-speed rail is used to define frequent service between major population centers located from 200 to 600 miles apart (or 320 to 965 kilometers) on trains that travel on dedicated tracks at speeds of at least 150 mph (or 240 km/h).
Richard Nunno, July 19, 2018, Transportation: Fact Sheet | High Speed Rail Development Worldwide, https://www.eesi.org/papers/view/fact-sheet-high-speed-rail-development-worldwide
In the United States, there is not yet a fully high-speed train line, and none are being built except in California.The Acela Express, running between New York and Washington D.C., reaches a top speed of 150mph on limited portions of its route, but its average speed is only about 66 mph. California is in the process of building an HSR system, but the first phase, connecting San Francisco to Los Angeles and Anaheim, is not expected to be completed until 2029 (although some of the infrastructure is already being used). No other state or local jurisdiction has, at this time, allocated the funding to begin construction of high-speed rail. In Texas, studies are being conducted for a “Bullet Train” between Dallas and Houston, and advocates say that construction should begin in a year or so. In Florida, the Brightline service between Miami and Orlando is operational, but with an average speed of 80 mph, it does not meet the minimum speeds to be considered HSR (although plans for increased speeds are underway). In addition, Florida’s governor recently announced another potential HSR line between Orlando and Tampa.