Commuters getting on westbound Interstate 540 in North Raleigh on Tuesday morning will find new traffic lights on the on-ramp that are meant to moderate the flow of cars entering the highway.
The ramp meters have been used around the country for decades, but these are the first in North Carolina. If the experiment on I-540 goes well, the N.C. Department of Transportation will look to use them elsewhere.
The signals have been installed on four westbound on-ramps: Falls of Neuse, Six Forks, Creedmoor and Leesville roads. The lights will let one or two cars onto the freeway at a time during morning rush hour and other times of heavy traffic.
The idea is that putting some space between the vehicles leaving the ramp should make it easier for them to merge into traffic on the highway, improving the flow and reducing the number of accidents.
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NCDOT engineers don’t know when exactly the lights will come on; sensors in the pavement of the on-ramps will detect if traffic has gotten to the point where the lights are needed, said John Sandor, deputy division traffic engineer. When traffic thins out, the lights will automatically go off, Sandor said.
Those sensors in the pavement will also determine if traffic from the on-ramp is backing up onto the road and will turn the light green long enough to clear the backup. NCDOT’s traffic operations center will monitor the ramps via cameras and can manually adjust the signals if necessary as well.
The light systems cost $2.5 million to install on the four on-ramps, which includes some widening of the ramps and the software that can be used as other ramp meters are installed in the state.
Sandor said studies in other cities show that ramp meters can cut travel time in half on congested stretches of highway simply by making it easier for entering traffic to merge. The lights will help make the most of three-lane I-540 before it becomes necessary to add another lane, at the cost of tens or hundreds of millions of dollars.
“Ramp meters are kind of a tried and true method to maintain interstate flow,” Sandor said.
State Highway Patrol troopers will be parked alongside the ramps the first week or so and may issue warnings or tickets to drivers who fail to stop at a red ramp lights. Sandor said NCDOT knows many drivers are skeptical about the lights, but he said the experience in other cities is that they work.
“It will become a normal function of life,” he said. “It’s just a traffic signal.”
Researchers at N.C. State University will compare traffic movement and accidents on the ramps before and after the signals to help NCDOT determine how well they are working. If they’re deemed a success, DOT has a list of other on-ramps in the Triangle where it will consider installing them, Sandor said.