U.S. Route 20 (US 20) is an east-west U.S. Highway in Pennsylvania, which clips the northwestern corner of the state, running entirely in Erie County. While it is part of the nation's longest road, it features the shortest segment of any two-digit U.S. route in the commonwealth. Although bypassed by Interstate 90 (I-90) as the primary through route in the area, heavy traffic has led to nearly the entire highway being upgraded to four lanes in width.