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What Are The Benefits Of Ramp Meters?

MINNEAPOLIS (WCCO) -- It's a part of your commute that might seem like it's slowing you down. But in reality, it's actually speeding things up and keeping you safe.

If you've hit the road on Twin Cities highways, you've likely noticed that traffic volume is nearly back to pre-pandemic levels. The Minnesota Department of Transportation said it's only off by about 5%.

Ever the more reason the mini-stop lights you see along on-ramps, known as ramp meters, are getting heavy use again.

"I'm sure that they help get the flow of traffic a little bit more consistent where it like normally would bottleneck," said driver Becca Thomas, after admitting they can at times feel annoying. "See people stopping for longer than they need to or when there's one car and not a line. It creates a line, kind of causes things to back up a little bit."

What are the benefits of ramp meters?

"It helps with the overall traffic flow of the system. Keeps things moving better. Reduces that congestion and then overall delay," said Brian Kary, director of traffic operations at MNDOT's Regional Transportation Management Center (RTMC).

The meters prevent congestion by breaking up what he calls "platoons of cars" from all entering a highway at once.

"If all those vehicles enter at the same time, people on the mainline have to slow down, and that's what really kind of triggers that congestion and triggers those breakdowns in traffic flow," he said.

The meters aren't running all day. They turn on during the rush hour periods, from 5:30 a.m. to 10 a.m., and 2 p.m. to 7 p.m.

But just because they're on doesn't mean drivers will always be stopped. Kary say most of them won't begin controlling traffic immediately when rush hour starts.

"There's traffic sensors on the roadway that will kind of measure the amount of traffic that's out there. And every 30 seconds that meter is determining, 'Do I turn on, or don't I turn on?' And then when conditions are right, that's when the meter will activate," he said.

Ramp Meters
(credit: CBS)

RTMC staff can manually turn them on as well. They'll do so for large events, like Vikings games on a Sunday, or to control traffic if there's a crash or construction.
The time interval between red and green lights is constantly changing as well. We watched one ramp meter light cycle last 15 seconds near Dale Street and Interstate 94 in St. Paul. Within a few minutes, the light cycle was down to three seconds. That's because the meters are getting real-time updates on the traffic on the main highway, as well as how many cars are on the ramp waiting for the meter.

"If that ramp looks like it's gonna start backing up onto the cross street, that will also cause [the meter] to start to speed up so that we don't interrupt that cross traffic even if the mainline can't handle it," he said.

What would happen if they turned off all the ramp meters?

"I'm sure it would be chaotic," said Thomas.

"I think it would be a lot of backed up traffic. And angry drivers," said driver Shanese.

In 2000, state leaders were curious as well. The Minnesota Legislature commissioned MnDOT to do a study to analyze ramp meter effectiveness and identify the public perception of metering. All 430 meters were turned off for six weeks. It evaluated traffic flow and safety impacts.

The results of the study found there was a 22% increase in travel times, a 7% decrease in freeway speeds, and a 26% increase in crashes.

"It showed that they really did work," said Kary.

It was after that study was completed that MnDOT decided to create the specific time slots in which the meters turned on during weekdays. It also influenced them to change the meters so they wouldn't allow traffic to back up on the ramps and into local streets.

Some meters were also removed after the study, specifically the ones that were installed on ramps that connected one freeway to another.

In the two decades since the study was completed, other meters have also been removed. Kary said about half were taken out or have yet to be turned back on along I-35W between Highway 36 in Roseville and Lake Drive in Blaine. That's because an EZ Pass lane was added to I-35W, which increased the flow of traffic, lessening the need for several meters.

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