Skip to main content

Could a Diverging Diamond Interchange be coming to Southeastern North Carolina?

It's not every day that a driver gets to legally drive on the "wrong side of the road".  But if a recent NCDOT proposal for the US 74/76 interchange with NC 133 in Leland is approved, Brunswick County motorists will be able to do just that.

The DOT is considering building a "Diverging Diamond Interchange", also known as a DDI, as a replacement of the current and heavily congested diamond interchange when the US 74/76 causeway is widened in 2013.  The DDI is one of a few possible plans for the interchange when the $19 million project begins.

A diverging diamond is unique as the travel lanes on the surface road- in this case NC 133 - are flipped to the opposite side before and after the interchange.  This flip is controlled by a traffic light at each end.  Traffic to and from the interchange ramps also intersect at the signals. 

The result is left turns onto and off of the interchange ramps now go unimpeded - that is the driver does not have to worry about crossing traffic in the opposite direction when making the turn.  Also, the only traffic signals needed are the two at the location of the 'flips'.

In 2009, Missouri was the first state to install the 'diverging diamond'at MO 13 and Interstate 44 in Springfield.  A photo of the completed project is below. (Source: Missouri Department of Transportation)

Missouri installed this interchange as it saved nearly $4 million compared to building a higher powered traditional diamond with additional turning lanes.  With NCDOT putting together every possible penny that they can find, the DDI will be a very high possibility.  Missouri also boasts a lower accident rate at the MO 13/I-44 interchange, a reduction of 50 percent.

In addition to cost advantages, the DDI allows for interchanges to remain below capacity longer.  They are maximized if there is a high volume of left turns on a lower speed surface road with space limitations. 

There are drawbacks, however.  On the surface route, both sets of signals cannot be green at the same time for both directions.  The flow of traffic will be more controlled and through traffic - in this case on NC 133 - will have to come to at least one stop when going through the interchange.  And of course the obvious concern - motorists who would be confused and unfamiliar with the new traffic pattern.

Since construction of the diverging diamond in Springfield in 2009, a handful of DDI's have been constructed throughout the country.  If this DDI is built in Leland, it will be North Carolina's second constructed DDI.  The first, located on I-77 at Exit 28 in Mecklenburg County, is scheduled to open in 2012.

Story Link:
New interchange design considered on NC 133 in Leland ---Wilmington Star-News

(HT: Joe Babyak)

Comments

James Dunlop said…
The one in Leland would be anywhere between the first and seventh DDI in the state. The Cornelius one looks like it'll be sometime in 2013 instead of 2012, and there's three projects in Concord, two on 85 and one on the last new section of 485. These three are actually let to contract, although the Design-Build schedule puts them in late 2013/early 2014.

Another one in Kernersville on I-40 and one in Lumberton on I-95 are being worked on, however their schedule will most likely be behind the others. Right now, any one of these could be the first one completed. I'm betting on the two on I-85 in Concord, based on the construction schedules I've seen. Cornelius could slip in ahead of those, though.

Jim Dunlop
Anonymous said…
MODOT just opened another DDI, I-270 at Dorsett Rd, in St. Louis County, last week.
hotrod6147 said…
Was the new bridge at Old Kingsdale Road completed? Was this simply a bridge, or an interchange?

Popular posts from this blog

Tulare Lake returns

During the winter of 2023 California experienced one of the wettest seasons in recent decades.  Enough snow and water were deposited into the Sierra Nevada Mountains that the runoff was enough to partially reform Tulare Lake within San Joaquin Valley.  Tulare Lake was once the largest lake west of the Mississippi River by surface area.  Tulare Lake has been largely dried for the past century due to irrigation divisions and upstream impoundments.  This blog will examine the history of Tulare Lake and its recent return.  Pictured as the blog cover is Tulare Lake from 19th Avenue in Kings County during early May 2023.  Tulare Lake can be seen near its maximum extent below on the 1876 P.Y. Baker Map of Tulare County .   Part 1; the history of Tulare Lake Tulare Lake is the largest remnant of Lake Corcoran.  Lake Corcoran once covered much of the entire Central Valley due to being it being located at a in natural low point from where mountain run-off would accumulate.  Lake Corcoran is thou

Former US Route 101 through Sargent

  Sargent is a ghost town and siding of the Southern Pacific Railroad located in southern Santa Clara County.  The original alignment of US Route 101 was aligned through Sargent via what is now known as Old Monterey Road.  Sargent was bypassed gradually due to shifts of the alignment of US Route 101 which occurred during 1941 and 1950.  Pictured as the blog cover is a view on Old Monterey Road which is now no longer accessible to the general public.  Below is a scan of the 1935 Division of Highways Map of Santa Clara County which depicts the original alignment US Route 101 through Sargent.   Part 1; the history of US Route 101 in Sargent Sargent lies on land which was once part of Rancho Juristac.  During 1856 James P. Sargent purchased Rancho Juristac and plotted what was known as Sargent Ranch.  By 1869 the Southern Pacific Railroad coast line reached the relocated town site of Gilroy.  The Southern Pacific Railroad coast line would be constructed through Chittenden Pass by 1871 whic

California State Route 60/Former US Route 60/70 through the Moreno Valley Badlands west to Riverside

This past month I drove California State Route 60 through the Moreno Valley Badlands westward towards the City of Riverside.  CA 60 through the Moreno Valley Badlands was once part of the corridors of US Route 60 and US Route 70. The present route of CA 60 is a 70 mile (76 counting multiplex) slice of former US 60 between downtown Los Angeles east to I-10 near Beaumont.  The vast majority of CA 60 aside from a small section in the Moreno Valley Badlands is presently a freeway grade. For me CA 60 holds some personal history as it was the route I used most frequently accessing work sites in the Inland Empire circa 2011-2013.  Despite what many others probably would say I always really enjoyed the Moreno Valley Badlands portion of CA 60.  Considering I frequently worked on US 60 through Arizona and New Mexico the route holds even more appeal.  I even have a CA 60 shield hanging up in my garage. Part 1; History of Roadways in the Moreno Valley Badlands CA 60 between B