Known as Piney Branch Road, the highway runs 2.84 miles (4.57 km) from Eastern Avenue at the District of Columbia boundary in Takoma Park north to MD 650 in Adelphi.

The state highway originally extended from downtown Silver Spring to White Oak and connected with U.S. Route 29 (US 29) at both ends.

MD 320 begins at the intersection of Piney Branch Road and Eastern Avenue at the District of Columbia boundary in the city of Takoma Park.

[1][2] MD 320 parallels the city limits to Mississippi Avenue, where the highway fully enters the unincorporated area of Silver Spring.

The highway continues east as a four-lane road with a center left-turn lane, crossing Long Branch before intersecting MD 193 (University Boulevard).

[3] The portion of this highway from modern US 29 to Carroll Avenue was paved by Montgomery County with state aid as a macadam road by 1910.

[6] MD 320 was extended north as a 18-foot-wide (5.5 m) macadam road from Carroll Avenue through Prince George's County to White Oak in 1931 and 1932.