Georgia State Route 400

Georgia State Route 400 (Georgia 400, SR 400) is a highway in the U.S. state of Georgia, concurrent with U.S. Route 19 (US 19) from exit 4B until its terminus just south of Dahlonega. SR 400 goes from Atlanta, at Interstate 85 (I-85), to Buckhead, Sandy Springs, Roswell, Alpharetta, Cumming, Dawson County, and Dahlonega. Like the Interstate Highways, it is a limited-access road (with exit ramps instead of intersections), but unlike the interstates (which were renumbered by the GDOT in 2000), the exit numbers do not indicate mileage: they still go up sequentially one-by-one. Once SR 400 passes exit 17 (SR 306), it changes from a limited-access expressway into an at-grade divided highway with traffic lights, but still with a high speed limit of 65 miles per hour (105 km/h) and ends at the J.B. Jones Intersection at SR 60 in Lumpkin County.

Between I-85 and I-285, SR 400 is designated "T. Harvey Mathis Parkway"; upon reaching the Perimeter (I-285) and beyond, the highway is designated "Turner McDonald Parkway". SR 400 is known locally as the "Georgia Autobahn", the "North Georgia Autobahn", or the "Alpharetta Autobahn" due to the prevalence of speeding.