Known as King Street, the state highway runs 1.64 miles (2.64 km) from U.S. Route 258 (US 258) north to an entrance to Langley Air Force Base within the independent city of Hampton.

SR 278 begins at a diamond interchange with US 258 (Mercury Boulevard).

The state highway heads north as a five-lane road with a center left-turn lane through a residential area.

The state highway gains an additional lane northbound before reaching its northern terminus at a gate for Langley Air Force Base.

North of the gate, the roadway crosses the Back River to reach the main body of the military installation.