Most major U.S. highways don't exceed a 6 percent grade, the magic number for the preferred maximum steepness of a road. Parleys Canyon (I-80) has a maximum grade of 6 percent.
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Ffordd Pen Llech, a winding street through the historic part of town, has a gradient of 37.45%. Resident Myrddyn Phillips, who took the measurements that led to the world title, said: “To have the steepest street in the world, recognized by Guinness World Records, is brilliant for Harlech, it's brilliant for Wales.”