The Olathe City Council unanimously approved a $567,375 agreement with engineering firm HNTB for additional work on the city's largest-ever capital project: the I-35 and Santa Fe Street interchange reconstruction.

The council previously approved a utility relocation agreement with Evergy Metro on Sept. 1 as part of the council's consent agenda, according to the Olathe Reporter. The HNTB agreement covers bridges, retaining walls, drainage structures, and traffic control and sequencing. The council also approved a utility relocation agreement with Evergy Metro for the project.

What it costs and who pays

City council documents put the overall project cost at $199,277,738, the Olathe Reporter reported. The Kansas Department of Transportation (KDOT) will cover $159,277,738. The remaining $40 million comes from city general obligation bonds.

That figure differs from the Johnson County Post's July 2026 reporting, which described the project as costing $285 million based on a city council presentation. The reason for the difference is unclear.

City staffers called it the largest capital project in Olathe's history.

The Johnson County Post reported in October 2024 that the project was on track to receive $98 million in federal infrastructure grant money, citing a news release from Gov. Laura Kelly's office. At that time, the total cost was described as more than $200 million.

What's being built

The "I-35 Santa Fe Forward" project spans two overlapping efforts, according to the city's project page. KDOT is managing I-35 widening and reconstruction between Santa Fe and 119th Street. The city is rebuilding the Santa Fe interchange.

Improvements include a reconstructed interchange at I-35, auxiliary lanes from Santa Fe to 119th Street, widening of the Old 56 Bridge, the flyover bridge connecting Old 56 Highway to northbound I-35, to two lanes, roadway widening and extension, and installation of traffic signals, medians, streetlights and sidewalks.

The new interchange will be a single-point urban interchange (SPUI), similar to the one at I-35 and 87th Street in Lenexa, the Johnson County Post reported. That design allows left-turning traffic to move simultaneously through one central signal, according to the city.

When construction starts

Auxiliary lanes on I-35 are tentatively scheduled to begin construction in late 2026 or early 2027, according to city council documents. The Santa Fe corridor and interchange work is tentatively scheduled to start in late 2027.

Utility relocations have already begun and are expected to continue through 2027. The city demolished several buildings adjacent to East Santa Fe Street between North Clairborne Road and North Lindenwood Drive in March 2026 to clear the way.

The biggest disruptions are still years off. In coverage published in July 2026, the Johnson County Post reported that Assistant City Engineer Therese Vink told the council in June there would not be full road closures during the utility relocation phase. The most significant traffic impacts are not expected until 2029, when Santa Fe Street will close completely for interchange reconstruction, the Johnson County Post reported.

During the KDOT portion of the work, drivers should expect several ramp and bridge closures lasting three to six months each, the Johnson County Post reported. The intersection of Mahaffie Street and Old Highway 56 will stay open, according to city officials.

In Johnson County Post coverage published in October 2024, Mayor John Bacon said of the project: "We know our residents want and need a faster, safer route through the heart of our city."

The entire project is expected to wrap up in 2030.