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From 2020 to 2025, Stonebrooke Engineering supported Rice County and MnDOT District 6 to redesign the CSAH 46/TH 19 intersection near I-35, which is a critical link for commuters and freight between Northfield, Lonsdale, and the Twin Cities in Webster Township. From the outset, coordination was key.

A Complex Design Challenge

The project team faced unique geometric constraints and high traffic demands. Through detailed analysis and collaboration, they developed an innovative solution: a single-lane, six-legged roundabout. This design accommodates all traffic movements, improves mobility, and reduces delays at a construction cost of $4.73 million.

Funding and Coordination

Rice County and MnDOT secured funding through the Minnesota Freight Program, Highway Safety Improvement Program (HSIP), and Local Partnership Program (LPP), supplemented by local CSAH and Local Option Sales Tax funds. Later, funding transitioned to Federal Surface Transportation Block Grant (STBG), Federal HSIP, and County contributions.

The Stonebrooke team worked closely with Rice County, MnDOT District 6, State Aid, the Geometric Design Support Unit (GDSU), and MnDOT Central Office to navigate an unusually complex approval process. Although delivered under the State Aid Delegated Contract Process (DCP), the design also had to meet MnDOT Trunk Highway and Interstate standards, satisfy federal requirements, and adhere to multiple program deadlines.

Environmental Challenges

A Phase I Environmental Assessment revealed a former gas station site, raising contamination concerns. Stonebrooke collaborated with MnDOT and Braun Intertec to complete a Phase II assessment, confirming the site was clean and avoiding costly delays. MnDOT’s environmental review also flagged potential impacts to the northern long-eared bat. To mitigate this, the team arranged winter tree clearing, hiring a specialized service to complete tree clearing after the environmental document was approved but before the project was bid. Additionally, permanent lighting was designed with downcast, cut-off luminaires to minimize light spill and protect wildlife.
 
Innovative Construction Staging

Construction began in April 2024, with traffic opening to the new roundabout in October 2024 and final completion in September 2025. BCM Construction, Inc. served as the general contractor. Maintaining traffic on TH 19 throughout construction was a major achievement. The team designed a temporary bypass through a corridor reserved for future I-35 expansion, enabling roundabout construction without full closures. Daily inspections, proactive communication, and continuous traffic control monitoring ensured safety and minimized confusion.

Interagency Collaboration

This project stands out for its innovative roundabout geometry, creative traffic staging, and seamless interagency coordination, setting a new benchmark for complex interchange design in Minnesota.

Stonebrooke Engineering

Stonebrooke is a renowned firm for surveying, planning, design and construction services with prequalifications in several MnDOT areas including roundabout design, geometric layouts, environmental documents (Class II), and transportation planning and a strong history of partnering with reputable companies to deliver quality products. Stonebrooke’s experienced team applied advanced engineering principles to design with safety, capacity, operational efficiency, and public acceptance at the forefront. Stonebrooke’s innovative design approach ensures appropriate entry deflection, central island sizing, and approach curvature to manage speeds appropriately. Key technical considerations for every project include design vehicle accommodation, sight distance, pedestrian circulation, drainage, and context-sensitive solutions. Stonebrooke Engineering is headquartered in Burnsville, Minnesota.