Prescott City hears 15% design review for SR 89 widening and effluent pipeline after repeated pipe failures

Prescott City Council held a study session Aug. 26 to review 15% design concept plans for the SR 89 corridor between Willow Lake Road and Fippin Trail, and to discuss replacing a failing 24‑inch effluent pipeline that runs under the road.

Public Works Director Gwen Roich said the immediate priority is the pipe, which the city has recorded more than eight failures in the last 2½ years and about 10 in five years. “The number 1 priority is the pipe. That pipe continues to fail,” Roich said, noting past closures that disrupted travel.

The design review presented three top alternatives developed by consultant Kimley‑Horn: Alternative 3B, a five‑lane widening through the corridor (budgetary estimate $36.7 million); Alternative 5B, a five‑lane/partial four‑lane barrier configuration ($35.5 million); and Alternative 2B, the top non‑widening option ($25.2 million). All alternatives include safety improvements such as extended tapers at the Fippin roundabout, consolidated access points, improved sight lines and right‑out/left‑in access controls near Willow Lake.

Nut graf: The study session focused on whether to use the construction window created by replacing three 24‑inch pipes in the corridor to also widen SR 89, or to rebuild the pipeline while keeping the current two‑lane cross section. Staff said widening would allow staged construction that preserves traffic flow; a non‑widening approach would require longer closures during pipe work.

Staff, engineers and council members discussed public input, modeling methods, environmental concerns and funding. Tim Sherwood, the city’s capital program manager, described the procurement and consultant team: Kimley‑Horn led design, with Lion Engineering and Waterworks on wastewater engineering, Colin Nicholas on rock removal, T2 Utility Engineers on mapping, Beta PR on outreach, ETC on geotechnical and Wilming (cost analysis). Sherwood said Kimley‑Horn was selected after a qualifications process and presentation interviews.

On public engagement, Operations Manager Carrie Oberheim summarized themes from the ongoing 60‑day comment period (which runs through Sept. 9) and the project website sr89improvements.com. Staff said they received broad public concern about widening, and that the city formed a 15‑member Design Ranking Advisory Group whose value‑based pairwise rankings influenced a technical advisory committee that produced the three alternatives presented.

Several council members pressed staff and consultants on the non‑widening alternative (2B). Councilman Grady asked why 2B’s analysis did not more fully explore elements suggested by the public — such as flex lanes, traffic signals and other lower‑impact measures — and whether those options had been vetted. Andrew Baird of Kimley‑Horn said the team produced 15% concept plans for each of the three alternatives and that, among 20 total alternatives considered, flex lanes and signal options had been evaluated but ranked lower. “We generated a full 15% concept plan for all 3 alternatives,” Baird said.

Traffic engineer Ian Mattingly said Kimley‑Horn’s origin‑destination analysis found roughly 22,000 vehicles per day on the corridor; 46% of those trips are commuter trips and 54% are non‑commuter (shopping, appointments, dining and similar). Mattingly said the consultant used multiple data sources — ADOT counts, city annual counts, permanent count stations and the regional model — and ran more than 100 VSIM simulation runs (AM/PM and scenario permutations) to test operations and future conditions projected to 2050. The consultants used a 2.75% annual growth rate for long‑range modeling, which Mattingly said was the most conservative historic rate found in several datasets.

On roundabouts and signals, Mattingly and Roich said the traffic study compared roundabouts with signalized intersections and found roundabouts performed better under projected growth. Mattingly said national and local comparisons show lower rates of injury crashes at roundabouts versus comparable signalized intersections and that the study found roundabouts will delay failure longer than signals in higher‑growth scenarios.

Funding and phasing: Roich and Sherwood described how costs would be allocated under state law and current city policy. For the wastewater portion, the city’s last rate study anticipates ratepayers would cover about 80% of wastewater costs and development impact fees would cover roughly 20%. For roadway costs, the city’s 1% street sales tax and development impact fees are planned to fund widening: staff said about 70% of the street sales tax could apply to the widening alternatives and that the city currently has approximately $38 million budgeted across funds for the project. Roich said staff are pursuing additional regional and federal funding, including a possible congressional directed spending request ($7 million) and a SIMPO request ($4.9 million) for FY26.

Construction impacts and timing: Staff stressed that replacing three 24‑inch pipes in the corridor will be disruptive. Roich said a non‑widening approach likely requires road closures of four to six months or more at individual work zones because there is less room to stage traffic while installing pipelines, whereas a widening approach allows staged construction that can keep traffic flowing by building lanes first and then working on the utilities.

Other clarifications made during the session: the existing effluent is treated wastewater (not raw sewage) and the city reports breaks to the Arizona Department of Environmental Quality; the corridor’s right of way is generally 150 feet through most of the project and narrows to 100 feet past the box culvert bridge south of Keefef or similar landmark; preliminary estimates for rock removal to accommodate a four‑lane cross section are roughly 12 feet on each side in constrained areas; and roundabout operational issues at corridor ends are projected to emerge around 2034–2038 and can be addressed as targeted projects in future capital plans.

No formal council action was taken at the Aug. 26 study session. Staff noted the study session is the second of two study sessions required by the council resolution directing public outreach and design concept work; two public hearings are scheduled during voting meetings (the first at 3 p.m. on the same day and a second at 3 p.m. on Sept. 9) and public comments will remain open through Sept. 9 on sr89improvements.com.

Ending: Staff said they will continue design to the 15% level, post incoming public comments, perform additional modeling requested by council (including emergency vehicle simulation) and return with further analysis and a financial breakdown once the council narrows alternatives. The council adjourned the study session to reconvene at 3 p.m. for the voting meeting, where public comment cards were to be heard in order.