 US 15 continues north as a four-lane controlled-access expressway past the Monocacy Boulevard/Christophers Crossing interchange before leaving the city of Frederick by crossing Tuscarora Creek.The highway parallels the Monocacy River and has a junction with Biggs Ford Road on its way north to the hamlet of Hansonville, where the U.S. Highway intersects Old Frederick Road.US 15 crosses Fishing Creek to the west of Lewistown and is closely paralleled on the west by Auburn Road as the highway gradually approaches the eastern flank of Catoctin Mountain.