Isanti reviews roundabout redesign after new truck counts; staff recommends slightly larger center and added turn lanes

City staff presented a design-phase update to the proposed roundabout on Heritage Drive, saying new traffic counts and heavy-vehicle analysis prompted changes to the intersection geometry designed to reduce congestion and avoid semis blocking the intersection.

“So now that we, have been able to move into design phase of this project, we went and collected new traffic counts, kept track of the heavy heavy vehicle, the big truck counts ... and kinda came up with some tweaks to that original concept,” the presenter said, describing a shift from a mini roundabout with a fully concrete center to a slightly larger small standard roundabout with a planted center and surmountable curbs for truck tracking.

The principal modifications staff described are: increasing the roundabout diameter (moving away from the 75‑foot mini center to a larger standard layout), adding a full intersection at Credit Union Drive with a westbound left‑turn lane to divert some traffic away from the circulatory roadway, and adding a long turn lane into the Kwik Trip to reduce the number of vehicles entering the roundabout. Staff said the changes will let two lanes extend farther before merging into one and will reduce the likelihood of backups reaching beyond Bridal Union Drive at modeled peak events.

The presenter said model runs show the revised layout performs acceptably in peak conditions and that, despite the geometry changes, the updated design remains within the scope of previously discussed cost assumptions. He emphasized next steps: advance the project into 3‑D design (cross slopes, drainage and curb transitions) and begin identifying easements and right‑of‑way to acquire so land acquisition does not delay the grant timeline.

Several council members urged additional adjustments. Councilman Merrill criticized a prior external study and welcomed the city’s own counts: “that poor, poor job by that engineering firm to do that traffic study ... it makes our jobs a lot harder and less confident in our decisions,” he said, arguing for closer scrutiny of the model and striping assumptions. Multiple council members pressed staff to evaluate an acceleration/right‑out lane from Minco Drive onto eastbound Heritage; the presenter said he would examine whether striping or a defined acceleration lane could be accommodated and noted geometric constraints where the existing curb, trail and a lift station limit footprint expansion.

Councilors also raised safety and emergency-access questions. Staff said the revised radii and surmountable curb sections are intended to allow semis and emergency vehicles to navigate the roundabout if necessary and argued that the roundabout’s continuous‑flow pattern typically makes it easier for emergency vehicles to proceed than a stopped signal.

Staff reported the project had been provided to the county engineer for review and that the county board had the city’s memo in its packet, indicating parallel county review. The presenter asked council for feedback and said he would incorporate comments before moving into detailed design.

Next steps: staff will finalize 3‑D geometric details, identify easement and right‑of‑way needs and continue coordination with the county and the city’s grant contact so construction cannot be delayed by land acquisition requirements.