The highway runs 1.09 miles (1.75 km) from 16th Street at the District of Columbia boundary north to MD 97 within Silver Spring.

MD 390 is a six-lane divided highway continuation of 16th Street into Maryland and serves as a western bypass of downtown Silver Spring.

MD 390 begins at Blair Portal traffic circle at the boundary between the District of Columbia and Maryland.

The circle also includes junctions with Eastern Avenue, North Portal Drive, and MD 384 (Colesville Road), which leads to U.S. Route 29 in downtown Silver Spring.

North of the railroad tracks, Washington Metro's Red Line begins to run below the route and the state highway passes through an oblique intersection with Second Street.