New Cornelius Interchange Will Put You On Wrong
1:00 pm
Fri May 20, 2011

New Cornelius Interchange Will Put You On Wrong Side Of Road (Sort Of)

If you're a regular on Interstate 77, you know rush hour can be a challenge.

Often exiting the highway can be the hardest part - Exit 28 in Cornelius is one example. But there's a plan to address the problem through a new concept that may change our interstate driving experience. It's called the diverging diamond interchange.

Exit 28 is about what you'd expect. You pull off on a ramp on the right side of the road, and you either get in the left- or right-hand turning lane. How long you wait depends on the time of day.

At 4:30 on a weekday afternoon, Tyler Beardsley stands near the corner of I-77 and Catawba Ave. He's the Town of Cornelius project manager.

"The exit ramp from (I-)77 northbound is backed up halfway down the exit ramp for cars trying to turn left," Beardsley said. "Backup on Catawba Avenue is going almost across the bridge to the other light for the other (I-)77 exit ramp."

Beardsley said it's not even the busiest time of day - the morning rush hour is worse.

"It's probably a 7- to 10-minute wait just to turn left to get onto the highways," Beardsley said.

The town and the state department of transportation have decided to makeover the exit and build what's called a diverging diamond interchange, or DDI in transportation-speak. The major difference is on the bridge over the interstate.

If you're on I-77 and don't take Exit 28, nothing changes. But here's how it works if you do exit there:

"You would basically just come up the exit ramp the same," Beardsley said.

The right lane would merge into traffic like normal.

"The left lane will be more of a free flow lane, or a yield lane, similar to a right-hand turn," Beardsley said. "You wouldn't have to cross over the other lanes of traffic like you do now - like a normal left-hand turn."

All you do is veer left.

"Instead of being on the right-hand side, you'll be on the left-hand side," Beardsley said.

Think: driving in England.

To help, there'll be a concrete barrier that separates traffic moving in opposite directions. Once you reach the other side of the interstate bridge, you come to a stoplight. When the light turns green, you then cross back to the right side of the road. It works because, in theory, traffic is always moving off the exit ramp.

If you're still a little confused, don't worry. You're in good company.

"I did not understand it until I went out to Missouri and actually looked at it and drove through it myself," Beardsley said.

Missouri is home to three of the five diverging diamond interchanges in the country. Beardsley and some of the other town staff traveled to the first in Springfield.

It only took six months to build, and drivers immediately got used to it, said Don Saiko of the Missouri Department of Transportation.

"Normal backup each day was about a mile," Saiko said. "During heavy times - if you had like a fourth of July weekend, we had two to three mile backups. Now we're experiencing none of that."

In addition to wiping out traffic jams, he said the new interchange has cut the number of collisions in half.

A few years ago, Cornelius officials were thinking it would cost upward of $35 million to revamp the interchange. Then two of the town's consultants on construction projects mentioned the diverging diamond interchange. It's cheaper - it would only cost about $4.5 dollars - and studies had shown it works.

Town Manager Anthony Roberts said he thought - there's an idea. He checked in with Jim Dunlap of the department of transportation.

"Once it came to us, I'm going, "Gee why didn't we think of that?'" Dunlap said.

This week state and town officials teamed up at Cornelius Town Hall to explain the concept to residents.

Dunlap kicked off the informational workshop by screening a video that showed how the interchange works.

Cornelius resident Dick Brolin attended the workshop. He commutes to work in Mooresville, and he's sold on the idea.

"It's a very logical approach once you wrap your head around it," Brolin said. "I think once you travel it, you'll find it's so much easier just to make your way through the interchange."

There's another benefit - it's safer for pedestrians and bikers. Down the center of the bridge there'll be walkway protected by concrete barriers.

Construction is still about two years away, but it's expected to only take six months to complete. State officials are also planning a diverging diamond interchange at the Poplar Tent Road exit off Interstate 85 in Concord.

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