The Lakewood Freeway portion of this highway was, at one time, slated to become designated as Interstate 420 (I-420), but that project was cancelled.

After curving to an east-northeast direction, and then beginning an east-southeast routing, it crosses over Big Indian Creek.

The highway enters Bowdon and curves back to the east-northeast just before intersecting the northern terminus of Elm Street.

Just to the east of Griffins Alley, it curves to a due-east direction and intersects SR 100 (Wedowee Street/North Carroll Street).

At an intersection with Maple Street, which leads to downtown Carrollton, SR 166 turns to the right onto what is essentially a bypass of the main part of the city.

It passes to the south of Sunset Hills Country Club and then reaches the Wayne Shackelford Interchange with US 27/SR 1/SR 16 (Martha Berry Highway).

They curve to the east-southeast and cross over the Chattahoochee River into southern Fulton County on the Dick Lane Bridge.

The highways curve to the southeast and leave the city limits of Sandtown and enter those of Atlanta.

They pass Southwest Atlanta Christian Academy and just north of Ben Hill Park.

Less than 0.5 miles (0.80 km) later, the Arthur B. Langford Jr. Parkway designation begins, and then they have an interchange with Interstate 285 (I-285; Atlanta Bypass).

Just over 2 miles (3.2 km) later, along the Atlanta-East Point city line, they have an interchange with DeLowe Drive and Stanton Road.

[4] By the end of the third quarter of 1921, SR 16 was designated from the Alabama state line, west of Bowdon to Carrollton.

[2][3] By April, it was extended across the Chattahoochee River and paralleled SR 41 to the east as it entered Atlanta on Campbellton Road, and intersected US 29 at Dill Avenue, farther north than it does today.

Also, the proposed eastern terminus was extended to I-20 between its crossing of Sugar Creek and its interchange with Gresham Road.

[44][45] SR 166 was originally supposed to extend (as I-420) from I-20 near Douglasville in the west to the DeKalb County seat of Decatur in the east.

[citation needed] The eastern portion of this was fought bitterly by residents in court, and was eventually cancelled, along with a number of other interstate highways in Atlanta.

south of downtown Atlanta, merging at an interchange with proposed I-675 and traveling northeastward on to I-20 near Gresham Park.

SR 166 Conn. begins at an intersection with US 27/SR 1 on the northern edge of Carrollton, where the roadway continues as Columbia Drive.

The highway leaves the city limits and travels on a nearly due east direction until it intersects SR 113.

It travels in a southeasterly direction and crosses over the Little Tallapoosa River, where it re-enters the city limits of Carrollton.

[50] The highway was proposed in 1998 on a routing from Shady Grove Road to its current eastern terminus.