Georgia State Route 400

Georgia State Route 400 (SR 400; commonly known as Georgia 400) is a freeway and state highway in the U.S. state of Georgia serving parts of Metro Atlanta. It is concurrent with U.S. Route 19 (US 19) from exit 4 (Interstate 285) until its northern terminus south-southeast of Dahlonega, linking the city of Atlanta to its north-central suburbs and exurbs. SR 400 travels from the Lindbergh neighborhood in the Buckhead district of Atlanta, at Interstate 85 (I-85), to just south-southeast of Dahlonega. Like the Interstate highways, it is a limited-access road (with interchanges instead of intersections), but unlike the interstates (which were renumbered by GDOT in 2000), the exit numbers are not mileage-based, they are sequential. Once SR 400 passes exit 18 (SR 369), it changes from a limited-access freeway 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/SR 115 in Lumpkin County.

Between I-85 and I-285, SR 400 is designated "T. Harvey Mathis Parkway", after a local land developer and road proponent who died the day after being appointed as head of the Atlanta Committee for the Olympic Games in June 1991, when the tollway was under construction. Upon reaching the Perimeter (I-285) and beyond, the highway is designated "Turner McDonald Parkway".

SR 400 is one of only two state routes in the 400–499 series to not be designated as an unsigned route following an interstate, with the other being the SR 410 near Stone Mountain . Although, both SR 400 and SR 410 were originally planned as interstate routes, SR 400 was supposed to be I-485 and SR 410 was supposed to be I-675.