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Planning Commission reviews how traffic impact analyses are built and when they’re required
Summary
Staff and a traffic consultant briefed the Planning Commission on TIA methodology — level‑of‑service grading, peak‑period selection, signal timing and study‑area scope — and discussed how counts, ITE trip rates and SHA coordination inform developer mitigation and planning decisions.
At its June 18 meeting the Calvert County Planning Commission held an educational work session on traffic impact analyses, focusing on the methods used to determine intersection performance and mitigation needs. An outside traffic consultant explained that level of service (LOS) grades intersections and approaches from A (best) to F (worst) and that county policy treats LOS C as acceptable for county and town‑center roads, while SHA (State Highway Administration) roads typically use LOS D as the adequacy threshold. "So for county roads and town center roads, that the level service of C is considered, at an adequate C or better," the consultant said.
Commissioners pressed the presenter on data sources and modeling choices: traffic counts are generally collected in 15‑minute increments by observers or video, then analyzed to identify the worst hour; trip generation for proposed developments is estimated from the ITE Trip Generation manual and distributed across a defined study area. The consultant said many TIAs now use Synchro and micro‑simulation tools and that calibration and field observations are used to align model outputs to real conditions. Commissioners raised concerns that county study areas (often one or two miles) can undercount regional through‑traffic and that adaptive signal timing primarily helps off‑peak irregular congestion rather than daily peak commutes.
