Motorists who want to get on Ga. 400 might have to wait in line.

Beginning Wednesday, there will be a stop light, called a ramp meter, at the McFarland Road entrance ramps onto 400 south and north.

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

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

“We’ll monitor these new ramp meters very carefully,” said Georgia Department of Transportation Traffic Engineer Scott Zehngraff. “If traffic starts to back up on the ramp, sensors will speed up the meters to allow more vehicles to move through. If our cameras show traffic spilling out onto the surface streets, we can turn them off completely.”

There are currently about 170 ramp meters throughout metro Atlanta, said department spokeswoman Teri Pope. They reduce average rush-hour commute times and reduce fuel consumption, merging accidents and vehicle emissions, she said.

If the meter at Exit 12 is successful, Pope said the same could come to other exits, saying the department “is always looking at additional locations where ramp meters can aid congestion.”

Pope said there will be signage on the ramp to warn drivers about the meter. Pope said vehicles currently entering the highway do so in a disorderly and potentially dangerous manner, often forcing their way into travel lanes causing additional stop-and-go congestion.

Pope said this creates a breakdown of free-flowing traffic near entrance ramps, causing a ripple effect for many miles.

“There will be a short learning curve period in the first few days as motorist adjust to following the meters,” Zehngraff said. “We realize that we may need to tweak them.

“Please bear with us, and keep in mind that there is no one ‘silver bullet’ solution to eliminate congestion. Ramp meters are just one of several tools that can help fight congestion.”