US 78 travels through portions of Haralson, Carroll, Douglas, Cobb, Fulton, DeKalb, Gwinnett, Walton, Oconee, Clarke, Oglethorpe, Wilkes, McDuffie, Columbia, and Richmond counties.

They cross over Buck Creek, and begin a very gradual curve to the east-northeast, shortly before leaving the city limits.

They pass Louise Suggs Memorial Park and intersect Line Street, where they enter Cobb County and the city limits of Austell.

They travel in a roughly eastern direction before curving to the east-southeast and passing the Austell Campus of Chattahoochee Technical College and Davis Chapel Cemetery.

The three highway continue to the southeast and cross over the Chattahoochee River into Fulton County and the city limits of Atlanta.

The concurrency travels through the Brookview Heights neighborhood, southwest of Carey Park and Williams Elementary School.

A short distance later, they intersect SR 280 (locally known as Hamilton E. Holmes Drive to the south and James Jackson Parkway NW to the north).

Three blocks later, at the intersection with Argonne Avenue NE, US 29/US 78/US 278/SR 8 begin to skirt along the northern edge of Ponce de Leon Center.

At the intersection with North Highland Avenue NE, is the Plaza Theatre and Druid Hills Baptist Church.

Just past Clifton Road NE, they begin to skirt along the northeastern edge of Dellwood Park before entering Druid Hills.

Less than 1,000 feet (300 m) later, US 78, concurrent with SR 410 splits off to the east-northeast (known as Stone Mountain Freeway), while US 29/SR 8 travel to the north-northeast on Lawrenceville Highway.

Almost immediately after the interchange, the freeway passes under the Silver Hill Road overpass and begins to skirt along the northwestern edge of Stone Mountain Park.

At this interchange, they curve back to the northeast and meet the westbound lanes again, just before leaving the boundary of the park and entering Gwinnett County.

The freeway crosses over West Park Place Boulevard on the Forrest L. Adair II Memorial Bridge and curves to the east-northeast.

The concurrency passes Eternal Hills Cemetery; then, they enter Snellville, where they intersect SR 124 (Scenic Highway) at the James D. Mason Memorial Interchange.

[3] (After the highway was expanded to four lanes in 1985 and rerouted near the Walton/Gwinnett border, the unexpanded portion formerly part of US 78 was renamed Logan Drive.)

Approximately 2 miles (3.2 km) later, they curve to the northeast have an interchange with the eastern terminus of SR 10 Business (East Spring Street), where the freeway bypass ends.

They meet an interchange for SR 10 Loop (Athens Perimeter Highway) and the southern terminus of Epps Bridge Parkway.

They pass east-southeast of Stegeman Coliseum, begin to curve to the northeast, and cross over the North Oconee River near the Georgia Museum of Art.

Southeast of the University of Georgia Farm Lake, the highways cross over Dry Fork Creek into Wilkes County.

In the city, just west of the intersection with the northern terminus of Campbell Street, the mainline routes begin to curve to the east-southeast.

Just after they intersect Stagecoach Road, they skirt along the eastern edge of Belle Meade Country Club and then the Thomson–McDuffie County Airport.

They leave the unmarked city limits and curve to the east, before coming back to the south-southeast and intersect SR 223 (White Oak Road).

The concurrency curves to the northeast and then back to the east-southeast, before they cross over Boggy Gut Creek and enter Columbia County.

At the southeastern edge of the city limits, the roadway becomes known as Gordon Highway, which is a major urban corridor farther to the east.

A few thousand feet later, they curve to the northeast, crossing into Richmond County (and the city limits of Augusta), and begin paralleling the northern edge of Fort Eisenhower.

About halfway between here and the interchange with I-520 (Bobby Jones Expressway), the three highways leave the edge of Fort Eisenhower and begin to transition into an urban corridor.

After the interstate, the roadway enters the main part of Augusta, passing south of Aquinas High School, and curves to the south-southeast, past the location of the now-closed Regency Mall.

A short distance later, they pass to the east of Old Medical College and the Old Government House, then they have an interchange with US 25 Business/SR 28 (Broad Street).

It showed, before 1947, US 78 routed along the current length of US 278 from Atlanta to the Belvedere Park–Avondale Estates city line, and SR 10 from that point to just north of Stone Mountain.