BY THE NUMBERS: DIVERGING DIAMOND INTERCHANGES
2009: the year the United States’ first DDI opened (Springfield, Mo.)
63: amount of DDIs nationwide
13: amound of DDIs in Missouri
23: amount of states with a DDI or planning to implement one
3: amount of states with one under construction
9: amount of states with a DDI in advanced design
9: amount of states where a DDI is being studied
30: amount of conflict points at a standard diamond interchange
24: amount of conflict points at a Single Point Urban Interchange (Monroe’s Ohio 63 exit)
18: amount of conflict points at a Diverging Diamond Interchange
A new kind of interchange design could be coming to Interstate 75's Union Centre Boulevard exit to help alleviate traffic in and around the area.
Dubbed the “diverging diamond interchange” — or DDI — and already in use at 63 interchanges nationwide, the design is aimed at boosting safety and enhancing overall operations, according to the Butler County Engineer’s Office, which presented the idea to trustees during a Tuesday work session.
The design directs traffic to criss-cross to the left side while passing over the interchange bridge for the sake of better and more continuous traffic flow, according to Matt Loeffler, a BCEO traffic engineer.
Traffic lights would hold oncoming traffic during each crossover stage.
“If you’re traveling from Muhlhauser Road heading east and you just want to go straight through over to (The Streets of West Chester) to go see a movie at the theater, as you approach the current intersection you would go over to the left side through a signal to the left side of the bridge,” Loeffler said.
The design also allows free flowing left turn movement like a typical right turn movement onto the interstate, he said.
“It’s intuitive,” he said. “If you know you need to go north, you’ll be in the left hand lanes to make your movement.”
Advantages to such an interchange include alleviating congestion, eliminating left-turn conflicts and reducing the amount of conflict points created via left-turn and straight-through movements, Loeffler said.
Such an interchange also creates the opportunity to safely accommodate pedestrians via a center walkway and creates a “calming effect” on vehicles because motorists reduce speeds while navigating the interchange, he said.
It also would reduce lost time and increase capacity, Loeffler said.
Potential challenges or disadvantages to such an interchange include coordinating the Muhlhauser Road signal to the new design, as well as driver unfamiliarity, the potential for wrong-way maneuvers at crossovers and the inability for off-ramp traffic to re-enter the freeway when drivers mistakenly exit at the interchange, he said.
The DDI envisioned for Union Centre Boulevard is comparable to one that opened in October 2013 at Interstate 270 and Roberts Road in Franklin County, Ohio.
“It seems to work very well,” said Matt Bruning, press secretary for the Ohio Department of Transportation, which initiated and carried out the project. “When you first look at it, you’re like ‘Wait a minute, what is this?’ but then you drive through it and it’s like ‘Oh, this makes total sense.’ “
Admittedly, it’s a “different traffic pattern than people are used to seeing,” but it has managed to eliminate vehicles backing up onto the interstate, something that’s commonplace at the Union Centre Boulevard interchange.
“Before they put this in, you’d have traffic back up because you’d have people trying to turn left to go north or south on I-270 from Roberts,” Bruning said. “You’d get a green arrow and then you’d get two or three cars through and now you’re waiting, so everything backs up. With this new traffic pattern, there is no more waiting to turn left because it crosses you over and gives you a chance to just turn left without having to go against traffic.”
The concept has caught on nationwide, with 23 states already having at least one in place, three states with one under construction, nine states where a DDI is in advanced design and nine states where a DDI is being studied.
Popular Science magazine referred to DDIs as one of the best innovations of 2009 in the engineering category for its “Best of What’s New 2009” issue.
Since opening in 1997, the Union Centre Boulevard interchange has been a catalyst for growth around the interchange and the township. But with the growth has come increased backups at the interstate.
Traffic along Union Centre Boulevard from Muhlhauser Road to Interstate 75 has increased 11.4 percent, going from 26,180 vehicles per day in 2004 to 49,000 in 2012, according to Butler County Engineer's Office traffic counts. Traffic east of the northbound exit/entrance ramps numbers jumped 47 percent between 2002 and 2012, going from 13,600 vehicles per day to 20,000.
Butler County Engineer Greg Wilkens told trustees the interchange is a conceptual design at this point, but asked them to endorse it as an idea so his office could pursue it further.
“We think it’s a good concept. It serves the area well and provides some of the things you’re interested in,” Wilkens said.
All three trustees offered their support.
“I think we’re overdue for this interchange, for these improvements,” said Trustee Lee Wong.
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