The portion south of MD 3 served as a primary segment in the western corridor connecting Baltimore–Annapolis, until the construction of Interstate 97 (I-97) in the late 1980s.

MD 450 heads west as Defense Highway and southeast as West Street toward an interchange with U.S. Route 50 (US 50)/US 301 (John Hanson Highway) and Annapolis; the east leg of the intersection is an entrance to the Westfield Annapolis shopping mall.

North of Bestgate Road, the highway leaves the commercial area, curves to the northwest, and reduces to two lanes.

MD 178 continues northwest and passes the historic home Belvoir before heading northeast of the Anne Arundel County Fairgrounds and entering the center of Crownsville.

In the village, the highway passes St. Paul's Chapel at the corner of Crownsville Road, which leads south to the grounds of the seasonal Maryland Renaissance Festival.

MD 178 continues northwest past the Rising Sun Inn and Sunrise Beach Road, which leads to another riverside community, Arden-on-the-Severn.

[3] The highway is so named because it was traveled by George Washington on his journey from New York to Annapolis, then acting as the capital of the United States, to resign his commission as Commander-in-Chief of the Continental Army in December 1783.

[6] The first portion of MD 178 to be constructed was a small segment of concrete road south from the southern end of Old Generals Highway at Iglehart by 1923.