TH 169 and CSAH 4 Preliminary and Final Design Project, Sherburne County, MN

The TH 169 and CSAH 4 Preliminary and Final Design project analyzed and designed a new grade separated interchange in the City of Zimmerman within Sherburne County. The existing at grade signalized intersection of TH 169 at CSAH 4 has significant safety and operational concerns.

TH 169 is a principal arterial serving 33,800 vehicles per day (2,200 HCADT). CSAH 4 is a minor arterial roadway serving 16,700 vehicles per day. Mobility is greatly underserved, especially during seasonal peaks when queues extend a mile in length along TH 169 and three quarters of a mile along CSAH 4. Many travelers find alternate routes to avoid congestion on TH 169, putting unnecessary demand on the adjacent north-south corridors. Growth projections for 2045 anticipate 51,000 vehicles will pass through this intersection every day. Travel reliability will be greatly compromised without improvements. The TH 169 and CSAH 4 intersection and intersecting corridors will become gridlocked with backups ranging from two to nearly four miles, resulting in thousands of trips rerouting onto the adjacent system.

This intersection is also one of the most dangerous in Minnesota with 101 crashes between the years of 2015 and 2019. The intersection crash rate is more than four times higher than the statewide average and the fatal and serious injury crash rate is six times higher than the state average. The most frequent crash type is rear ends (77 of the 101 total crashes) demonstrating the signal and resulting backups are the primary contributor to the safety issues at the intersection.

TH 169 provides a critical link between the Twin Cities Metro Area and Central Minnesota, serving residents, businesses, commuters, and tourists. Following the completion of the Elk River 169 Redefine, CSAH 4 will be the only remaining signal on Highway 169 between Highway 10 in Elk River to Onamia.

This project considered several interchange alternatives, going back to a preferred concept from a study completed in 2007, alternatives that rose or lowered CSAH 4, alternatives that lowered TH 169, and an in-depth review of three interchange designs that kept CSAH 4 at grade with TH 169 going over it. The City of Zimmerman expressed a desire to minimize property impacts while maintaining access to TH 169.  All alternatives except those keeping CSAH 4 at grade with TH 169 going over it were dismissed due to the significant property impacts these concepts would have.

The three interchange alternatives that were analyzed in-depth include a tight diamond interchange option with roundabouts, a single point urban interchange, and a combination of a diamond and partial cloverleaf interchange. All three options were found to significantly reduce crashes, traffic backups and delays, and improve pedestrian and bicycle facilities with safer connections. Ultimately the tight diamond interchange option with roundabouts was found to be the preferred option as it has the lowest amount of wetlands impacted, lowest amount of right of way impacts, and the lowest estimated construction cost. The existing condition of the intersection is shown in Figure 1 and a rendering of the preferred alternative is shown in Figure 2.

Access management was also considered with the proposed interchange. All intersections along TH 169 within a half mile of the ramp merge points will be closed. The proposed design also converts the intersections of Main Street at CSAH 4 and 3rd Street at CSAH 4 to right-in/right-out and installs a roundabout at 2nd Street and CSAH 4 to improve operations and accommodate the restricted movements. The proposed design also ties the intersection of Fremont Drive into the east interchange ramp terminal to create a five-legged roundabout while eliminating the existing T-intersection, which would have been within 700 feet of the interchange. The project is currently finishing up the final design phase with construction anticipated to start spring of 2025. 

As published in the North Central Institute of Transportation of Engineers (NCITE) Spring Newsletter.

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woman in black suit outside smiling at cameraKelsey Larsen is a traffic engineer who began her career in 2015. Her primary responsibilities include traffic analysis for intersection control evaluations, corridor studies, and preliminary and final roadway design projects. She is well versed in ITE trip generation, traffic distribution, and in using Synchro/SimTraffic and Arcady to evaluate existing and proposed conditions. Client satisfaction is a top priority for Kelsey, and she is always willing to go the extra mile to make sure projects are done right. She enjoys creating quality products for clients and strives to show information in a way that is easily understood by everyone.

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