Beltline drivers in Raleigh could soon see 'diverging diamond' at Western Blvd.
Posted September 13
Raleigh, N.C. — Drivers on Interstate 440 in Raleigh could experience some traffic headaches when the widening project through the western part of the city begins next year.
The North Carolina Department of Transportation is planning to use that opportunity to switch up the tricky interchange where traffic enters from Western Boulevard. The DOT hopes the new design will save money and lives.
The interchange between Western Boulevard and I-440 was designed back in 1959 for a much less-congested Raleigh. DOT engineer Jim Dunlop said its overdue for an overhaul.
"It's older than I am," Dunlop said. "It really needs to be replaced."
Dunlop specializes in managing congestion. One of the worst parts of the Western Boulevard and I-440 interchange, Dunlop said, is the tricky left merge from outbound Western Boulevard onto I-440 West.
He said the big beltline widening project in the next few years gives designers an opportunity to fix it. The most likely answer to the problem is what's called the diverging diamond interchange.
Here's how it works: Drivers turning right onto an interstate would stay in the right lane, while drivers turning left have to stop at a signal, switch over to the other side of the road and then turn left.
Drivers going straight just head through the signal.
Dunlop says the free-flowing left turn is safer.
"Injury crashes have gone down 40 percent," Dunlop said. "They've worked very well" in places, like Greensboro, where the DOT has employed the diverging diamond.
To build the diamond, engineers can frequently retrofit an interchange using the existing bridges, saving millions of dollars in some cases.
Dunlop said the style of interchange is the easiest on drivers, too.
"This is the concept the drivers have picked up the quickest," Dunlop said.
In a few years, drivers in Raleigh likely will get a chance to learn it for themselves.
The DOT is considering diverging diamond interchanges are some other locations in the Triangle. They're studying the option at I-440 and Wake Forest Road, Interstate 40 at Airport Boulevard and I-40 at N.C. Highway 42 near Clayton.