Missouri DOT Pioneers Divergabout and Wins Awards
A Cutting-Edge Solution: Missouri DOT Implements Innovative Divergabout at Congested US 50 and MO 291 Interchange
Local and state governments came together to update a highly congested 1960s-era interchange, pioneering a divergabout, a combination of a diverging diamond and a roundabout, at the U.S. 50 and MO 291 interchange, and winning awards for the innovation.
“This is one of the heaviest traveled interchanges in Lee’s Summit, during the peak period,” says Matt Killion, Area Engineer for the Missouri Department of Transportation (MoDOT). “We saw a lot of congestion.”
The condition of the bridge started MoDOT looking at the project, and initially, MoDOT planned to just replace the bridge. But then, in coordination with the City of Lee’s Summit, the state started to look for ways to improve safety, accessibility and additional capacity for motorists and pedestrians. After considering several options, it decided on the divergabout, which combines a roundabout at the north end of the interchange with a diverging diamond interchange at the southern end.
“MoDOT prides ourselves on using innovation to deliver solutions and improve safety,” Killion says. “This concept worked most efficiently, because it handled the peak travel movements the best and kept the outer road connections.”
A University of Missouri study of diverging diamond interchanges found reductions in motor vehicle accidents resulting in injury or death.
The city of Lee’s Summit was a major partner on the project, even though the improvements were limited to state-owned and maintained roadways. The city provided $8 million, funded through local bond proceeds, and it also secured $6.8 million in federal funds.
“We have a good relationship with MoDOT, and we have had many successful partnerships in the past with state infrastructure projects,” says Michael Park, City Traffic Engineer for Lee’s Summit. “As our City Council and mayor prioritized improvements in the city, the 291 Highway South junction with U.S. 50 highway was at the top of their needs, although it was not a local road.
Park reported a history of fatal motor vehicle crashes at the intersection and a desire to attract economic activity in the area just south of the interchange. The interchange also leads north into downtown.
“We felt something needed to be done,” Park says. “It was an older interchange. It was due for reconstruction, and rather than just replace the bridge, it was time to add capacity, improve safety and plan for many years to come.”
The city sought a bond issue to fund the project, which received strong citizen support. The city also secured federal funds, using the bond monies as local match.
“It’s in the middle of our city and impacts tens of thousands of our residents every day,” Park says.
MoDOT handled administration of the contract, construction inspection and design. It contributed $1.22 million to the project and the Mid-American Regional Council’s Surface Transportation Program funds provided $6.8 million.
GBA of Lenexa, Kansas, designed the configuration. GBA worked with TREKK Design Group of Kansas City, Missouri, on lighting and signal design. The design includes enough room to add an additional lane on Route 50 in the future.
Radmacher Brothers Excavating Co. of Pleasant Hill, Missouri, received the construction contract and began work in May 2017. The company was founded 35 years ago and focuses on heavy highway projects within 150 miles of Kansas City.
“We were able to finish it six months ahead of schedule,” says Ed Andres, with Radmacher Brothers.
Tight Deadlines While Maintaining Traffic
The original bridge was removed and replaced with two concrete-girder bridges, within the same right of way, eliminating environmental and utility issues. Retaining walls were added to the ends of the bridges to shorten their length.
Radmacher Brothers built the two bridges off line as traffic flowed on the original bridge. One was built on the east side and the other on the west side of the existing bridge, changing the alignment of the route. Once the bridges were built, plans called for temporary pavement while building the roundabout.
“We figured out a way to use the new bridges and close off the through movement northbound or southbound through the intersection,” Andres says. “We actually received emails saying traffic was moving better during construction than before construction.”
The divergabout enabled the DOT to add lanes on the ramps and eliminate two traffic signals. The department also added a pedestrian and bicycle path and maintained access to a park.
The contractor came up with an idea to shorten the length of time it would take to build the roundabout at the north of the project, by closing a portion of the interchange. After discussing it with stakeholders in the area, the department approved the change.
The project had originally been set with seven phases, Andres explains. Radmacher Brothers reduced the number of phases by four. The city agreed and set tight deadlines. The contractor completed that section of the project within 63 days, working seven days per week to complete the work on time.
“I’d like to give a lot of kudos to our construction workers who were able to get that work done,” Andres says. “They figured out things in the field to get it done in a timely manner.”
Most of Radmacher Brothers’ equipment has GPS and total station capabilities, eliminating the need for traditional staking.
“We were done with the project a whole lot sooner,” Killion said.
Positive Feedback and Accolades
This is the state’s second divergabout. The first was constructed at Interstate 49 and 155th Street in Grandview, Missouri. Radmacher Brothers also built that one, Andres says.
At the opening ribbon cutting ceremony, Lee’s Summit Mayor Bill Baird said he expects the improved intersection will attract business to the region. The traveling public has accepted the divergabout.
“We used best practices from both intersection types,” Killion says. “We have a lot of overhead signs to help drivers determine which lane they need to be in before making their turn. We have received a lot of positive feedback.”
Park called it “a very good project,” adding that he attributes its success to the city’s relationship with MoDOT and how well everyone worked together. “Everyone is pleased with the result.”
The interchange project has received numerous awards, including the Engineering Excellence Competition Honor Award from the American Council of Engineering Companies of Missouri, and an Excellence in Concrete Award from the Concrete Promotional Group.
“This project does what we set out to do,” Killion concludes. “We were able to keep traffic moving during construction and able to provide congestion relief, while staying within our existing footprint.”