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County proposes mini-roundabout at Stilson Ranch pathway to reduce speeds, improve sight lines
Summary
Teton County staff presented a concept and field-testing results for a mini-roundabout at the Stilson Ranch / Moose-Wilson pathway intersection to slow cyclists, improve sight lines at a tunnel mouth, and create a three-leg intersection; construction details, surface treatments and cost deltas remain to be defined.
Teton County staff on Aug. 4 described a proposed mini-roundabout at the Stilson Ranch intersection of the Moose-Wilson Pathway and Tim—9s Trail intended to slow users, reduce conflict at a curved tunnel approach and improve sight lines.
Brian Schilling, pathways coordinator for Town of Jackson and Teton County, presented the concept and described the site—9s existing problems: a high-speed sweeping turn into a tunnel and a blind approach where cyclists often cross center lines. Schilling said the Stillson Transit Center project provided an opportunity to relocate an adjacent pathway and redesign the intersection with improved sight lines.
Max Moran, parks and pathways project manager, described design elements intended to reduce speeds to a target of roughly 8 to 10 miles per hour: approach curves to force lower entry speed, textured and colored pavement for tactile and visual cues, a constrained 8-foot travelway around the roundabout to discourage two-way conflicts, and temporary center-island treatments (planters in summer; removed for winter maintenance) to allow performance testing before committing permanent features.
Staff performed field trials using cones and on-road tests at a larger site to observe negotiated entry speeds; Moran and Schilling said tests at 8 mph were easier to negotiate than attempts at 20 mph. Commissioners discussed design details including splitter islands on approach legs, directional arrows or stamped markings in the pavement and long-term durability of textured pavement under winter plowing.
Commissioner Gardner requested a cost comparison showing the delta between doing the roundabout now as part of the transit-center work and doing a simpler intersection now with a later retrofit to a roundabout; staff agreed to seek contractor estimates that include mobilization differences.
Moran said staged, removable center-island elements would allow the county to assess winter maintenance and vehicle maneuverability before installing permanent features. Staff also noted potential flexibility within existing easements to shift portions of Tim—9s Trail farther west depending on mapping and easement constraints.
