## How Fast is Fast?

The exact definition of "high-speed" isn’t, well, exact. European standards place it at more than 125 miles per hour, while U.S. definitions start at 90 miles per hour. The Acela Express—the Amtrak line stretching between Boston and Washington, D.C.—is perhaps the only "high-speed" rail line in the country. But while top Acela speeds reach 150 miles per hour, the train averages only about 88 miles per hour.