Merriam eyes ‘diverging diamond interchange’ at Shawnee Mission Parkway and I-35

A northeast Johnson County city is eyeing a replacement of one of the busiest corridors in the KC metro area in order to keep up with increasing demand.

The Shawnee Mission Parkway and Interstate 35 interchange sees almost 40,000 vehicles per day, and its traffic has been increasing annually, according to Merriam Public Works Director Celia Kumke. It also has some of the city’s highest crash rates.

In order to keep up with increased traffic and improve pedestrian accessibility, the city of Merriam conducted a study with HNTB Corporation to possibly replace the interchange and make some improvements at Antioch Road and Shawnee Mission Parkway.

“Future traffic volumes are expected to drastically exceed capacity,” Brent Gerard, a project manager at HNTB, told the City Council in February, adding that peak travel times would leave commuters in their car for more than two hours at the interchange if it’s left alone.

The city’s discussion on the needed roadway improvements comes at a time when hundreds of apartments, more businesses and a new Trader Joe’s are all popping up within city limits.

Specifically, the city is exploring a diverging diamond interchange as the solution — a type of interchange that briefly shifts traffic to the opposite side of the road in order to allow vehicles to turn left onto interstate ramps without crossing oncoming traffic.

“The DDI (diverging diamond interchange) and Antioch improvements will help Shawnee Mission Parkway significantly, but the drawback is you are going to put traffic on I-35 faster than you were before,” Gerard said. “It’s possible that it becomes your bottleneck without other work.”

However, the study found that a diverging diamond interchange would improve traffic times and reduce the number of crashes by 32 accidents per year.

Merriam isn’t alone in its roadway improvements. Further south, Olathe launched its own overhaul at the I-35 and Santa Fe corridor to improve infrastructure and prevent accidents. Demolition began this year, and construction is anticipated to last until the summer of 2030.

Like Olathe, Merriam’s reconstruction would be a massive undertaking.

HNTB estimates in its study that improvements at Shawnee Mission Parkway and Antioch would be $4.3 million and the diverging diamond interchange would range between $32 and $43 million.

However, Merriam needs federal funding and to establish a partnership with the Kansas Department of Transportation before anything could begin, Merriam spokesperson Ciera White told The Star.

“The project itself is still in very early stages,” White said. “Nothing has been decided if and when this project will move forward. The city is working on securing federal funding … That is the key in all of this. It could be in a few years from now it could not.”