Published: September 21, 2024 | Last Updated on September 24, 2024, 11:13 PM
OKLAHOMA CITY — When the May Avenue bridge over Northwest Expressway was closed in 2016 – the result of being hit by a semi pulling a boom lift – it shed a harsh light on something that Oklahoma City commuters had known for years:
That whole interchange has some serious problems.
Even following the major repair work that rebuilt and reinforced a section of the bridge, city officials began speaking more directly about the need to fully redesign and reconstruct the NW Expy and May interchange in a way that better accounts for safety, travel in either direction, access for cyclists and pedestrians, and above all, for increased city traffic.
In February of this year, the City Council discussed some possibilities and proposals for the $10 million project to redesign the area, and late last month, they narrowed those proposals to two potential designs: a diverging diamond interchange and a double roundabout.
Both are relatively recent, modern designs considered groundbreaking and innovative upon their first adoptions, and either one would be a first for Oklahoma City.
Complete overhaul
Recognizing the need for a complete reconsideration of the Expressway and May intersection, city officials set about fielding design proposals and narrowing down plans for the project, which is projected to cost around $10 million to be paid for from the city’s 2017 general obligation bond.
It’s expected to be a significant project aimed not only at improving driver safety and pedestrian walkability but also at providing drivers with more easily navigable options and routes in the area.
One example is that for a driver to currently travel from the eastbound lanes of NW Expressway to the northbound lanes of May Avenue, they’d need to exit onto May heading southbound and turn around.
Google Maps currently suggests an even more convoluted route, taking a left turn onto Mosteller Place, a right onto United Founders Blvd., and another left onto northbound May.
This complicated routing has been known to create confusion among drivers, particularly during rush hour periods when it can be difficult to merge between lanes on NW Expy.
In addition to the difficulty of navigation, there’s also a clear need for a higher clearance for the May Ave. bridge.
“The bridge is too low at 14’9” and gets hit frequently,” OKC Public Works marketing manager Shannon Cox told Free Press via text this week. “It’s being raised 2’ and we found this alternative way to tie back in and make it safer to get on and off NW Exp.”
An interview with the City of OKC Public Works Department staff about the designs and timeline was not granted.
But, officials with two other states that already have implemented the two designs being proposed were eager to speak about them.
Diverging Diamond Design
The first of the proposed options to address these needs is the diverging diamond interchange design (in the feature photo,) a groundbreaking design developed by the Missouri State Department of Transportation and first built and implemented in Springfield, MO in 2009.
The Missouri Department of Transportation won awards and recognition that year for their design.
OKC Free Press reached Eric Schroeter, assistant chief engineer with MoDOT, by phone to discuss the design. Schroeter has been with MoDOT for over 30 years and was on the team that helped design and implement the first diverging diamond interchange 15 years ago.
“We have a lot of them around the state now,” Schroeter said. “They don’t work everywhere, and the design has to meet the conditions, but there are a couple of significant advantages to the design.”
Primarily, the design is considered much safer for drivers because of the reduction in “conflict points.”
“A traditional interchange has about 30 conflict points, which is what we call places where traffic and cars cross each other, and each of those conflict points is a place for a potential crash,” Schroeter explained. “The diverging diamond takes that down to 18, so it reduces by almost half the number of places where traffic has to cross each other. So the potential for crashes is reduced just by the design itself.”
He explained that the design also makes more efficient use of the left turn lanes and turn signals and allows for multiple traffic movements to take place simultaneously.
And while the design may look especially complex from aerial views and diagrams, Schroeter said that drivers tend to navigate them easily.
“Drivers fairly quickly adjust to it,” he said. “The most common thing you’ll hear is that sometimes they feel like they’re driving on the wrong side of the road, but only for a short time. So we’ve done a lot of outreach and education about it and it’s important that the signage and pavement markings help guide people through.”
UPDATE — Since publication, a reader who once lived in Elk City, Oklahoma called a diverging diamond interchange to our attention where Elk City’s Main Street and I-40 intersect.
Double Roundabout Design
The other interchange design being considered is the double roundabout.
In a double roundabout, traffic signals are done away with entirely in favor of single-direction roundabouts routing traffic into turns and merges without the need for signals and more traditional intersections.
The double roundabout design allows for a more narrow bridge but may require more space on either end for the roundabouts to be constructed.
Ohio was one of the pioneering states for the double roundabout design, and Ohio Department of Transportation Press Secretary Matt Bruning filled us in on the design’s benefits via email.
“We know that roundabouts significantly reduce the risk of serious and deadly crashes,” he said. “One of the double roundabout locations, US 68/SR 15 and Lima Ave in Findlay has seen an 85% reduction in total crashes and 88% reduction in serious injury/fatal crashes. It was installed in 2020.”
That can be attributed to the design reducing the number of conflict points down to just 16, even fewer than the diverging diamond design, primarily because of the absence of traffic signals and traditional intersections, which could also mean a much lower maintenance cost for the city.
Bruning noted, however, that not all drivers are always receptive to the roundabout design.
“While there may be some opposition from the public on the front end, especially in areas where no roundabouts currently exist,” he said, “we have found that time and time again, people generally come around to the concept and like them.”
Extended Timeline
Designs and plans for the NW Expressway and May project are currently being considered by the City Council and City departments, but the potential timeline for the overhaul has changed from the original hopes.
According to reports in February of this year, the City’s timeline originally eyed a finalizing of plans by the end of 2024 and a beginning of work sometime in early 2025, but officials are now saying that timeline has been pushed back substantially.
“Plans for NW Expressway and May are at 60%” Cox confirmed in her text this week. “Plans won’t be completed until April at the earliest. Anticipate project to be ready to bid last quarter of next year.”
Brett Fieldcamp has been covering arts, entertainment, news, housing, and culture in Oklahoma for nearly 15 years, writing for several local and state publications. He’s also a musician and songwriter and holds a certification as Specialist of Spirits from The Society of Wine Educators.
