MD 478 begins at an intersection with MD 180 (Jefferson Pike) in Knoxville. Westbound MD 180 provides access to westbound US 340 toward
Harpers Ferry and
Charles Town. MD 478 heads east as a two-lane undivided highway through a forested area parallel to the
Potomac River,
Chesapeake and Ohio Canal, and
CSX's
Metropolitan Subdivision railroad line. The state highway crosses several streams that flow into the Potomac River. After passing through the community of New Addition, MD 478 enters the town of Brunswick, where the state highway ends at Florida Avenue. The roadway continues east as Potomac Street, the main street of Brunswick that passes through the
Brunswick Historic District. Potomac Street leads to Maple Street, which heads south to the historic
Brunswick station on
MARC's
Brunswick Line. All of MD 478, Potomac Street east from MD 478 to Maple Street, and Maple Street south to the train station are part of the
National Highway System as an
intermodal connector. ==History==