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County transportation director walks commissioners through traffic impact analyses
Summary
Jamie Oliver, Isle of Wight County Department of Transportation director, gave a step-by-step tutorial on Traffic Impact Analyses (TIAs), emphasizing VDOT’s technical role, data inputs (counts, trip generation), Synchro modeling outputs, and how commissioners should review TIAs' summary findings rather than appendix data.
Jamie Oliver, the county’s Department of Transportation director, presented a detailed tutorial April 28 explaining how Traffic Impact Analyses are prepared and how the Planning Commission should evaluate them.
Oliver said TIAs are technical studies prepared using professional best practices and VDOT guidance. “Isle Of Wight does not maintain separate guidance for how to do a TIA. We defer to VDOT specs and standards,” she said, adding that VDOT approves technical elements such as public-street acceptance and driveway entrances but does not decide land use. Oliver walked commissioners through data collection (traffic counts and peak-hour definition), trip-generation methods using the ITE manual, scenario building (existing, no-build, build), and model outputs (level of service, delay, queuing) produced by Synchro.
She emphasized practical review tips for commissioners: focus on the TIA’s executive-summary recommendations and whether those recommended improvements (turn lanes, signal timing changes, storage length) are reflected in the application’s proffers or conditions. Oliver noted that some differences in reported counts often reflect counting different road segments and that engineering judgment can be used for corridor-specific adjustments.
Commissioners asked about VDOT’s authority, timing of counts, updating older TIAs, and whether the commission can require longer projected build-out years; Oliver said many of those issues are resolved in prescoping and by coordinating assumptions between applicant, staff, and VDOT. She also discussed corridor studies (Brewers Neck, Ben’s Grant) as examples of when the county reviews long-term network effects rather than only project-level deltas.
Oliver’s presentation concluded with examples of model outputs commissioners should cross-check: the TIA’s summary tables, Synchro appendix sheets, signal-timing appendices, and VDOT comments; she recommended commissioners focus on conclusions and matching those to proffers rather than reading all technical appendices. The session included a robust Q&A and flagged that staff may request updated counts when a project’s data are older or if the corridor is high impact.
