High-speed rail systems are found all over the globe. Japan’s bullet train began operating in 1964. China will have 31,000 miles (50,000 kilometers) of high-speed track by the end of 2025. The fastest train in Europe goes almost 200 mph (320 kph). Yet high-speed rail remains absent from most of the U.S.

Stephen Mattingly, a civil engineering professor at the University of Texas at Arlington, explains why high-speed rail projects in much of the country so often go off track.

The Conversation has collaborated with SciLine to bring you highlights from the discussion, edited for brevity and clarity.

How is high-speed rail different from conventional trains?

Stephen Mattingly: With conventional rail, we’re usually looking at speeds of less than 80 mph (129 kph). Higher-speed rail is somewhere between 90, maybe up to 125 mph (144 to 201 kph). And high-speed rail is 150 mph (241 kph) or faster. There’s also a difference in the infrastructure for these different rail lines.

Is there anything in the U.S. that’s considered high-speed rail?

Mattingly: The Acela train operates in the

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