The idea of a north–south bypass of Hagerstown to relieve congestion on the contemporary main highway through the Hagerstown Valley, U.S. Route 11 (US 11), predates the Interstate system. Construction on the Hagerstown Bypass began in the mid-1950s and was completed in 1958 from US 40 north to the Pennsylvania state line. I-81 was assigned to the new freeway in 1959. The southern section of the freeway from the Potomac River to US 40 was built starting in 1962 and completed in 1966. Beyond interchange improvements, I-81 has changed very little from the four-lane freeway of the 1960s. Long-range plans call for widening I-81 to six lanes and effecting further interchange improvements along what is a major commuting and trucking corridor.