 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.