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City staff urge replacing Grapevine Crossing roundabout with signal ahead of large retailer
Summary
Public Works presented traffic modeling showing a two‑lane roundabout will be overwhelmed by the proposed big‑box retailer and future growth; staff recommended acquiring right‑of‑way and installing a signal before the retailer opens to avoid disruptive construction later.
Public Works staff told the Washington City Council on July 8 that a proposed large retail development at Grapevine Crossing will raise peak left‑turn volumes enough that the existing roundabout will not accommodate future traffic as reliably as a signalized intersection.
Paul Mogul, the city engineer, said the city hired Horox to run a VISM simulation of the roundabout and used SYNCHRO to analyze a signalized option, feeding both models with the retailer’s traffic‑impact study numbers. “Based on that analysis, Public Works recommends proactively replacing the roundabout with a traffic signal before the retailer is constructed,” Mogul said, adding the change would let the city avoid much larger traffic impacts and more difficult construction later.
Mogul told council the PM peak contains heavy left‑turn movements (he cited hundreds of left turns per hour on several legs) that, when combined with development‑driven volumes and future commercial growth, make dual left‑turn lanes and additional right‑of‑way necessary for a signalized layout. He estimated engineering, parts and construction timing could put the project roughly a year from decision to completion and said construction could take about four months.
Council members pressed staff on modeling assumptions and alternatives. Councilmember Coates and others asked whether the models account for other nearby projects and for signal timing or ramps controlled by UDOT; Mogul said staff used the retailer’s traffic inputs and that Horox’s microsimulation showed driver hesitation and conflicts the simpler analysis misses. Some members asked staff to analyze lower‑impact fixes — dedicated right‑turn lanes, different striping or adding a free‑flow right — before committing to removing the roundabout.
Several council members said they prefer to avoid removing a roundabout unless necessary. Councilmember Belliston said he liked the current roundabout and preferred delaying removal “until there is certainty that there is a big box need.” Staff replied the city has budgeted planning and right‑of‑way funds so it could move quickly if development proceeds.
Council direction: staff said they will analyze additional options (dedicated right turns, roundabout modifications, and impacts of upstream signal timing) and return with refined designs and right‑of‑way needs. No formal vote on a final design was taken at the meeting.
