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.

Potomac Street leads to Maple Street, which heads south to the historic Brunswick station on MARC's Brunswick Line.

[4][5] The highway was paved from Brunswick halfway to Knoxville in 1927 and completed in 1928.