Planning commission backs code requiring traffic impact studies at 25 trips, widens peak‑hour window

The Snyderville Basin Planning Commission voted Aug. 25 to forward a recommended amendment to county code that would require developers to submit a traffic impact study (TIS) when a project is expected to generate 25 or more net vehicle trips during defined peak hours. The commission added staff‑requested edits extending the morning peak window to 7 a.m.–10 a.m. and the afternoon window to 3 p.m.–6 p.m. before sending the recommendation to county council.

Eva De Larnes, a county transportation planner, told commissioners the proposed threshold relies on the Institute of Transportation Engineers (ITE) trip generation rates adopted in county ordinance 9‑58 and that sample calculations show 25 net peak trips is typically reached only by larger uses such as supermarkets, fast‑food nodes or gas stations. "So I I'm saying all of this to give kind of a context for 25 net trips is actually quite a lot," she said, adding that the county already charges transportation impact fees and uses the TIS for mitigation planning when appropriate. Commissioners asked how credits for previous uses and pass‑by trips factor into the calculation and whether non‑profit or public‑benefit projects would be treated differently; staff said the study requirement would apply regardless of ownership while fee waivers remain a separate council process.

Commissioners debated whether the 25‑trip trigger is the appropriate lever to require studies. "Is 25 a good number, or should it be a little lower?" Commissioner Mooney asked, noting some building types can be large without triggering the TIS. Staff responded that 25 is an industry practice (used by Park City and others), that UDOT and regional agencies use different thresholds for different contexts, and that codifying a trigger gives staff the authority to require studies rather than relying on informal negotiation. The commission voted by voice to forward the edited amendment to the county council for their consideration.

What happens next: County council will receive the commission’s recommendation and the proposed code language. If council adopts similar language, developers whose future proposals meet the threshold will need a licensed engineer‑prepared TIS before an approval that would trigger mitigations paid by the applicant. The commission’s recommendation also asks staff to provide a clear TIS checklist on the county website to standardize submittals.