I-55 Corridor Improvements Design-Build

Challenge

Congestion, safety and reliability of I-55 south of St. Louis led MoDOT to seeking a design-build team. Adding a third lane in each direction was the focus of the project, but the system-to-system interchange between US 67 and I-55 was the heart of the challenge. The current cloverleaf is plagued by tight weaving configurations that create congestion and safety concerns.

Solution

The unique interchange concept developed by the Bartlett & West Team maintains two of the loop ramps—one as a single lane and the other will be enhanced to a dual-lane loop. The other ramps through the interchange are being reconfigured with a continuous-T concept that utilizes roundabouts instead of signalized intersection. 

Another substantial improvement is a new interchange being added at US 67 and Route CC. The current signal backed US 67 traffic onto I-55. The interchange configuration was complex due to the development and tight right-of-way around the intersection. The new interchange will be a tight-urban diamond with walls in each quadrant of the interchange to keep within right-of-way. To create a grade-separated interchange, US 67 will be lowered by over 15 feet, which will improve sight distance and reduce grades along US 67.

The project also includes addressing the Route Z and McNutt interchanges with I-55 as well as minor improvements at the Route A interchange. The most significant change at these three interchanges was at Route Z, where the outer road is closely spaced to the ramp terminal in the southwest quadrant. The new interchange includes a large roundabout that consolidates the ramp terminal and the outer road at one intersection.

An innovative maintenance of traffic scheme was utilized to allow the contractor to add the third lane and rebuild the current passing while maintaining two lanes in each direction throughout construction.
 

Value

The design-build project significantly enhances I-55 by adding a third lane for seven miles, effectively relieving traffic congestion and improving roadway reliability. This upgrade ensures a safer commute for all drivers. Additionally, the project impacts five different interchanges and involves the rebuilding or rehabilitation of 27 bridges, further contributing to the overall improvement of the infrastructure. The original concept included a fly-over bridge, but Bartlett & West was able to achieve the same level of service while avoiding a costly fly-over bridge. This allowed the design-build team to offer additional improvements, such as addressing more bridges through the corridor and completely rebuilding the current passing lane, which provided more value to MoDOT.