The first section of I-81 to be constructed in Maryland was the pre-Interstate Hagerstown Bypass that was planned to provide relief to the existing north–south highway through downtown Hagerstown, US 11. The highway was planned to run from US 40 west of downtown Hagerstown to the Pennsylvania state line, where the Pennsylvania Department of Highways would continue the bypass north to tie into US 11 near Greencastle. Preliminary engineering on the Hagerstown Bypass began in 1954 and construction began in 1956, by which time a southern extension was planned south to US 11 east of Williamsport. The freeway was completed from US 40 (now MD 144) to the Pennsylvania state line in 1958, including an interchange with the present alignment of US 40 west of downtown Hagerstown, a highway that was completed around 1963. Traffic from the Hagerstown Bypass followed Mason Dixon Road to US 11 until the bypass was extended into Pennsylvania and tied into US 11 around modern Exit 3 in 1960. The new freeway was marked as I-81 beginning in 1959.