While only a secondary state highway, it serves as a major thoroughfare through southern Fairfax County, acting as the main street through Springfield and Franconia, as well as serving Burke, West Springfield, and Rose Hill and connecting them towards Alexandria and Huntington near the Potomac River.

SR644 then crosses Pohick Creek and enters West Springfield where it intersects with SR 638 (Rolling Road).

The road continues east and eventually crosses Accotink Creek and enters Springfield.

[1][2] After passing through the interchanges, SR 644 continues east through Springfield then crosses over the Washington Metro Blue Line and RF&P Subdivision into Franconia, acting as the main thoroughfare through it.

After crossing South Van Dorn Street, SR 644 enters Rose Hill and narrows to four lanes and then down to two at the center of the CDP.