Engineers present preferred ‘skewed roundabout’ for Highway 141/Towner Drive interchange; cost opinion about $28M

Wade Greiman, a transportation engineer with Snyder & Associates, presented planning and environmental linkage (PEL) study findings and alternatives for a proposed interchange on Iowa Highway 141 at Towner Drive.

Greiman said traffic along the corridor rose from about 25,000 vehicles per day in 2016 to nearly 33,000 in 2023 and that projections range from roughly 50,000 to 62,000 vehicles per day by 2050. He said crash analysis for 2019–2023 identified 47 crashes at study intersections, 42 crashes in the segments between intersections, 13 injuries and one fatality; that crash pattern and operational concerns drove consideration of geometric improvements and access control changes. The team evaluated five alternatives and identified a skewed roundabout/dog-bone-style interchange as the preferred alternative because it reduces conflict points, supports traffic operations and minimizes impacts to the golf course east of the corridor.

Greiman said the project is about 80% complete for the PEL study and the PEL will be submitted to the project management team in mid–late June; field work for the federal NEPA review has already begun. He presented a January cost opinion of $31,850,000 and an updated, more recent cost opinion of about $28,000,000, while cautioning that numbers are estimates. He outlined funding sources already procured or identified, including $3.4M in STBG through the MPO, about $1.1M from a carbon reduction program (CRP), $1.205M committed via the city's predesign agreement with Iowa DOT and $3.2M from Iowa DOT; he said federal BUILD and RAISE/RISE grant opportunities and congressional community project funding applications have also been pursued.

Council members asked technical questions about capacity, how a roundabout would operate for high-volume movements, pedestrian and bicycle accommodations (a planned 10-foot trail across the relocated Towner), landscaping budgets and what ‘funding secured’ means. Greiman explained that many federal transportation funds are reimbursement-based (agencies obligate funds but projects are typically reimbursed after expenditure), that multilane roundabouts can handle higher volumes (roughly 30,000–40,000 ADT for two-lane roundabouts depending on movements and phasing), and that construction could begin as early as 2028 if sufficient funding is procured.

No formal council action was taken; council thanked the team and asked staff to continue coordination through the PEL and NEPA processes.