Council reviews Silver Summit interchange study, weighs SPUI vs. dual roundabouts

County staff and consultants presented the Silver Summit Interchange Study to the Summit County Council on April 5, outlining traffic counts, future forecasts and two primary design alternatives for handling anticipated growth around Kimball Junction and Silver Creek Village.

The study team — including Brandon Brady and Carl Miller (county transportation), Gary Horton (Wall Consulting Group) and Charles Mason Hill (UDOT) — told the council that traffic counts taken last October show routine morning queuing at the southbound off-ramp at US-40 and Silver Summit Parkway and that, under a full-build 2030 scenario, three of four studied intersections would operate at unacceptable levels without improvements.

The report evaluated seven design alternatives and focused on two recommended options. The Single-Point Urban Interchange (SPUI) would reconfigure ramps and require rebuilding the bridge structure, delivering higher long-term vehicle capacity but at substantially higher cost and a longer implementation timeline. The dual-roundabout alternative would reuse more existing structure, deliver safer outcomes for pedestrians and bicyclists in most scenarios, and be less expensive to build and phase, though it would rely on future additional access points to sustain performance under very large buildout scenarios.

Council members asked detailed questions about maintenance responsibilities, pedestrian and bicycle accommodations, costs and timing. Staff said signals introduced by a SPUI would create a new maintenance obligation that the county does not currently staff for; counties sometimes contract with UDOT to operate cabinet-level equipment. Staff also described phasing possibilities: a traffic signal or a roundabout at the southbound off-ramp could be built in the near term; a full SPUI would require rebuilding the interchange bridge and likely federal involvement.

Cost estimates presented to the council showed wide ranges reflecting alternative scopes. The SPUI-level scope was described in the presentation as an approximately $77–88 million project when all ramps, signals and a new structure are included. The dual-roundabout options were shown in a $48–78.5 million range depending on whether future alternative access points were included. Staff emphasized these are planning-level estimates.

Several council members said they favored pursuing the roundabout option and adding future access points to reduce single-point dependence on the interchange, because dual roundabouts can be phased and still allow later upgrades. Members repeatedly urged staff to ensure grade-separated or otherwise safe pedestrian and bicycle connections if roundabouts are chosen. Staff agreed pedestrian connections were part of the conceptual designs and that mid-grade separated tunnels or bridges were being considered where required.

Councilors also discussed property and plat implications. A pending land transfer and plat amendment for the Marketplace at Silver Creek (an exchange of roughly three acres referenced in the staff packet) may not provide sufficient right-of-way for the most robust roundabout footprint shown in the study. Several council members urged staff to meet with the developer and Horrocks/Wall Consulting promptly to determine whether the current agreement and exhibits need amendment before recording final plats, to avoid future rework and increased costs.

Staff asked the council for direction on which alternative to pursue for budgeting and preliminary design. Councilors indicated a preference for a phased approach that starts with southbound improvements that can be implemented quickly while preserving options for later capacity expansions. Staff and UDOT reiterated that federal approvals would be needed for any changes that modify interstate interchanges, and that additional studies would be required to add full new interstate access points.

Next steps: staff will coordinate with UDOT and the developer to refine right-of-way requirements, pursue near-term improvements at the southbound off-ramp, and return with a recommended funding and phasing plan.