WRAL Investigates: Is the Triangle's first diverging diamond interchange safe?

The Triangle’s first diverging diamond interchange opened last year at Western Boulevard and Interstate 440. The criss-cross traffic pattern was a new experience for many drivers headed to North Carolina State University’s campus or downtown Raleigh. WRAL Investigates found the opening came with some bumps in the road.

"Over-engineered, definitely over-engineered," says driver Jon Mitchell, who routinely used the Western Blvd. exit to get to work. He’s not a fan of the new traffic pattern, "I know people don’t like changes, but I don’t understand why you gotta cross traffic right there when you had easy flowing traffic."

According to the North Carolina Department of Transportation website, diverging diamonds are "easy to navigate, eliminate last-minute lane changes, and provide better sight distance at turns, resulting in fewer crashes. The design reduces congestion and better moves high volumes of traffic without the need to increase the number of lanes…"

We found the new free-flowing traffic may have been too free-flowing. The trouble spot was on eastbound Western. When the eastbound traffic signal turned red, the light for vehicles coming off of the Beltline onto the same eastbound lanes turned green in about 1 1/2 seconds. However, even at full speed, it would take eastbound vehicles 3-4 seconds to reach that interchange. The timing greatly increased the risk for t-bone crashes.

WRAL Investigates obtained crash data from that particular block of Western Boulevard for the month of November. In the first two weeks, there was one crash. Once the diamond opened on November 16, there were four crashes, all in the eastbound lanes around that trouble spot.

Not long after we started asking the DOT questions, we went back out and found that 1.5 second light differential is now closer to eight seconds, allowing through traffic to easily clear the trouble spot. Based on our observations, the questionable light-timing was in place for at least a month. WRAL Investigates is now waiting for updated crash data.

DOT Communications Manager Marty Homan told us "Confirmed there were signal timing and pavement marking adjustments made following the opening. Everything looks good on paper, but we have to see it in the field and make adjustments as necessary."

That leaves drivers with diverging opinions. "I honestly kind of like it better than before because it stops the traffic and keeps things flowing," driver Myrell Holloway told us.

But for Jon Mitchell, it’s not a diverging diamond, but a diversion diamond. "It’s become so bad I don’t even take the Western Boulevard exit anymore."

There are now 14 diverging diamond interchanges across the state with more on the way. National studies have shown they do reduce crashes and the severity of injuries, especially after people get used to the new design.