Construction on the portion of I-81 south of US 40 began in 1962 to fill a gap between the portion of I-81 in Maryland and the portion of the Interstate completed between WV 9 near Martinsburg and US 11 southwest of Williamsport in West Virginia. MD 144's bridge over I-81 was constructed in 1963 once the relocated US 40 opened. The cloverleaf interchange between I-81 and the future I-70 was constructed in 1964, including the collector/distributor lanes. The remainder of the highway south to the Potomac River, including the bridge over the Potomac River, was under construction by 1965. The southern section of I-81 from the West Virginia state line to US 40 opened in 1966.