Innovative Interchange Design Leads to Project Savings for St. Charles County

The county had a vision of creating an additional north-south arterial route, that would connect to Route 364 allowing better access for local traffic, improvements to traffic flow along parallel routes and economic development.

Gutermuth Road, located in St. Charles County, Missouri, was a two-step project for GBA. Initially, GBA was hired by St. Charles County to conduct a location and corridor study along the Birdie Hills and Gutermuth Road corridors.

Studies and Analysis

GBA provided a feasibility study and conceptual layouts for alternatives to extend the Birdie Hills Road and Gutermuth Road corridors as future connections to Route 364. GBA did a thorough traffic analysis focused on traffic impacts, traffic flow, safety, cost and environmental impacts. During the study, designers created five possible solutions for Birdie Hills Road and Gutermuth Road, along with an evaluation of a new interchange connection to Route 364. Many of these solutions had multiple alternates, but the preferred solutions were analyzed for environmental and traffic impacts, as well as estimated costs to determine an optimal solution.

As the next step in the study, GBA was asked by St. Charles County to evaluate several configurations of a new interchange along Route 364 at Gutermuth Road. The team led a brainstorming session to weed out options that weren’t a  match for the desired location. During brainstorming, the team developed variations of four feasible interchange configurations. Part of the evaluation process included traffic analysis to verify capacity and geometric needs at the ramp terminals as well as evaluated project impacts.

Design and Funding

The final interchange layout included a dog bone roundabout design. GBA provided analysis to help the County determine between Surface Transportation Program (STP) or Congestion Mitigation and Air Quality Improvement Program (CMAQ) funding sources and provided input and data for the successful funding application. GBA developed preliminary, right-of-way and final roadway and bridge design plans for the interchange. During design, GBA provided a Traffic Safety and Operations (TS&O) Report, a CE2 document for National Environment Policy Act (NEPA) classification, floodplain hydraulics analysis and modeling, and a full traffic noise analysis study and design of recommended noise mitigation measures. The design also included widening part of the Route 364 bridge over Crooked Creek and utilization of the existing overpass structure to help minimize costs of the interchange.

Construction for this interchange was completed in 2020 for a cost of $5.2M, which provided a 23% savings from the County’s initial project budget.

Expansion Beyond the Interchange

Following construction of the interchange, GBA provided preliminary, right-of-way and final design for the reconstruction and expansion of Gutermuth Road just north of the interchange as a phase of the overall corridor study improvements. This one-mile segment of roadway improvements entailed realignment, profile changes, widening to three-lanes, staged traffic control, new shared-use paths, cross-road culverts and a new enclosed drainage system.

For additional information and project updates, visit—Phase-3.



St. Charles County

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