US 15 was expanded to a divided highway north of Frederick between 1972 and 1985. The U.S. Highway was expanded to four lanes from MD 355 at Harmony Grove to Angleberger Road in Lewistown in 1973. Four-laning of US 15 continued in 1981 when the highway was expanded from the intersection with St. Anthony and Orndorff roads south of Mount St. Mary's University to just south of the Pennsylvania state line near Emmitsburg. This section of divided highway was extended south through the MD 550 interchange in 1983. As part of this project, the oblique intersection with MD 806 on the north side of Thurmont was removed. MD 806 was moved onto Albert Staub Road, which was extended north over a new crossing of Owens Creek to its present terminus at Roddy Creek Road, where local traffic could access US 15 at a perpendicular intersection. The two-lane highway between Lewistown and MD 550 was expanded to a four-lane divided highway in 1985. The MD 77 interchange was completed with the construction of the southbound US 15 ramps in the southwest quadrant of the junction. A third interchange was added on the south side of Thurmont as a connector between US 15 and MD 806 in 1985 as well. US 15's expansion to a four-lane divided highway north of Frederick was completed in 1989 when the piece of highway at the Pennsylvania state line was expanded to four lanes contemporaneous with the four-laning of the Gettysburg bypass.