ST. LOUIS—The Missouri Department of Transportation broke ceremonial ground Friday on a $246 million plan to add a third lane to a busy 12-mile corridor of I-55 in Jefferson County.

The project awarded to KCI Construction and Bartlett & West will stretch from Route Z to U.S. Route 67 and will also include replacing 14 bridges and fixing 12 others along the corridor. An entirely new bridge will be built at a new interchange for I-55 and State Route CC, replacing what is now a signaled crossing.

According to MoDOT, approximately 70,000 motorists use the corridor daily, with 15% of that traffic coming in the form of heavy trucks.

“MoDOT is excited to partner with KCI Construction to deliver this $246 million project. Along with adding a third lane to Interstate 55 from Route Z to US 67, this project will alleviate the traffic bottlenecks in the corridor and will improve safety and reliability on both I-55 and US 67. It is an honor to be part of such a transformative project for Jefferson County,” said I-55 Project Director Justin Wolf in a news release.

The project is scheduled to be done in December of 2026.

The public can learn more about the project online at a dedicated MoDOT website.