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Helena staff show modeling for proposed roundabout at 11th/Last Chance; alternatives and costs discussed
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Summary
Transportation staff and consultants presented 65% roundabout designs and traffic-model comparisons for the intersection near 11th Avenue and Last Chance Gulch; commissioners asked for a narrower stop-controlled alternative and a detailed cost breakout, including utility upgrades.
City transportation staff on Aug. 27 presented 65%-complete designs and modeling that compare a roundabout, a signal, and several stop-controlled alternatives for the intersection that serves 11th Avenue and Last Chance Gulch.
Staff and their consultant showed side-by-side simulations for a signalized intersection, an all-way stop, an all-way stop with pedestrian enhancements and a roundabout using peak traffic and pedestrian counts. The materials incorporated Miovision camera data the city collected; staff said pedestrian volumes at the location have increased about 50% since earlier counts.
Transportation staff said the roundabout option reduces queuing compared with the current all-way stop, provides pedestrian refuge islands and lowers vehicle speeds. Staff said the proposed roundabout design was placed within existing right-of-way to avoid property acquisition; it would remove about three parking spaces on one approach. Staff told commissioners the roundabout offers gateway landscaping opportunities and functions if power is out.
Commissioners pressed staff for a focused estimate for a stop-controlled alternative that would include pedestrian-safety enhancements — splitter islands, refuge islands and lane-width reductions to roughly 11–12 feet — but omit the central island. Staff estimated a roundabout could be roughly $2 million to $3 million and said a stop-controlled pedestrian-enhancement package would likely be roughly $1 million to $2 million; staff said they would develop a more detailed cost breakout that separates surface improvements from any necessary utility upgrades beneath the intersection.
Staff noted other design items under consideration: reduced crossing distances, enhanced crosswalks and, where appropriate, rapid-flasher beacons. Public-safety considerations included additional proposed fire hydrants to improve coverage in the area; staff said three additional hydrants were proposed as part of utility planning. The transportation consultant said the project is on track for 90% plans in six to eight weeks pending agency review, after which permitting and bidding would follow.
