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City staff and engineers brief commission on traffic impact studies, ITE use and mitigation options
Summary
City staff and contracted engineers led a study session explaining traffic impact‑study components, thresholds for requiring studies, differences across zoning/subdivision/site‑plan stages, ITE trip‑generation use and limitations, mitigation options, and when the city may require applicant‑funded surveys or sensitivity analyses.
City planners and engineers presented an in‑depth study session on traffic impact studies, describing what those studies measure, when they are required, how they are scoped, and the commission’s role in evaluating them. Presenters said traffic impact studies are typically required when a proposed development is anticipated to generate more than 50 peak‑hour trips and that study scope increases from zoning to subdivision to site improvement plan (SIP) reviews.
Engineers Jacqueline and Lindy explained the technical workflow: establish parameters (study area, analysis years and peak periods), collect existing traffic volumes, model background traffic and horizon years, estimate trip generation and distribution (using ITE rates or field surveys), and test mitigations such as turn lanes or signal phasing to meet the city’s acceptable Level of Service (LOS) standard (individual movement LOS of D or better). The presentation included practical notes: ITE contains hundreds of land uses with variable sample sizes; staff may request local surveys or sensitivity analyses for new or nuanced uses; the applicant’s engineer prepares the study and the city engineer performs technical review and back‑checks calculations.
During Q&A, staff confirmed typical LOS delay thresholds for signalized intersections (A = 0–10s, B = 10.1–20s, C = 20–35s, D = 35–55s) and explained the city can require applicant‑funded counts or sensitivity analysis when assumptions materially affect mitigation timing or type. Presenters emphasized that a traffic study can conclude the existing network can absorb added trips with no mitigation; not all studies require off‑site improvements.
The session was technical and interactive; commissioners asked about accounting for post‑COVID travel patterns, third‑party delivery vehicle impacts, and how to handle uncertain timelines for roadway improvements in background traffic modeling. Staff suggested case‑by‑case approaches and potential updates to guidance if recurring gaps arise.
