The state Department of Transportation unveiled ramp meters this week at the McFarland Road (Exit 12) entrance ramp to Ga. 400.

The meters are operational before rush hour begins and at various times throughout the day, depending on traffic patterns.

When the meters are on, lights switch between green and red every three to five seconds, allowing one vehicle at a time to merge onto the highway.

DOT officials have said the meters, of which there are about 170 throughout metro Atlanta, reduce commute times, fuel consumption, merging accidents and vehicle emissions.

The department hasn’t ruled out adding the meters at other exits along the corridor.