US 340 was widened and resurfaced with bituminous concrete from Knoxville to the approach to new bridge at Sandy Hook in 1948. In conjunction with the construction of the Frederick Freeway, US 340's cloverleaf interchange with US 40 was built in 1954 and 1955. Jefferson Street in Frederick was widened in 1956. When US 40 was moved from Patrick Street to the Frederick Freeway in 1959, US 340's eastern terminus was moved from Patrick Street west to the new interchange. Construction on the US 340 freeway began when the highway's bridge across Catoctin Creek was built in 1961. This bridge came into use in 1964 when the freeway segment between the MD 180 interchange east of Petersville and the ramp from MD 180 west of Jefferson was opened, replacing the curvaceous old alignment at Catoctin Creek. The present alignment of US 340 opened as a four-lane divided highway from the Valley Road / Keep Tryst Road intersection in Sandy Hook east to Weverton also opened that year. The portion of the freeway between Weverton and MD 180 east of Petersville was under construction in 1964 and completed in 1965. MD 180 was assigned to old US 340 from Sandy Hook to west of Jefferson in 1965.