The Cobb County Department of Transportation (CCDOT) makes a recommendation of posted speed limits for radar and speed limit ordinances for review and approval by the Georgia Department of Transportation (GDOT) and the Cobb County Board of Commissioners. Only GDOT-approved speed limits may be enforced by Public Safety. The radar and speed limit ordinances are updated approximately every three years.
The criteria used to establish posted speed limits are based, in part, upon the characteristics of the roadways and their design speeds. The key elements include:
- Road alignment
- Sight distance
- Lengths of merges and tapers
- Road surface characteristics
- Shoulder condition
- Grade (i.e., steepness of the road)
- Roadside development
- Parking practices
- Driveway spacing
- Functional classification of the street
- Crash experience
Additionally, speed limits are established by drivers. In order for a speed limit to be effective, it must be reasonable and the majority of drivers must comply voluntarily. National studies have found that the speed at which 85% of motorists travel is reasonable and safe. This determination is made by conducting a speed survey of vehicles traveling along the roadway in question during normal operating conditions.