What Is a Traffic Impact Analysis?

In most contexts, yes. Traffic Impact Analysis (TIA) and Traffic Impact Study (TIS) describe the same process. Some agencies also use terms like Traffic Impact Assessment, Traffic Operations Analysis, Traffic Statement, or Transportation Impact Study. The name varies by jurisdiction, but the purpose is the same: evaluating how a development affects the surrounding transportation network.

In most jurisdictions, a TIA must be prepared by a licensed Professional Engineer (PE) with expertise in traffic operations. Many agencies also prefer or require a Professional Traffic Operations Engineer (PTOE) certification. Submitting a study without proper credentials will typically result in rejection during the review process.

Some jurisdictions allow TIA waivers in specific circumstances. For example, when the project generates fewer trips than the threshold, when a prior study already covered the site, or when the proposed use is less intensive than the previous use. Waivers are not automatic; they require a written request with supporting documentation and are granted at the discretion of the reviewing agency.

This is a common concern. TIA mitigation recommendations are negotiable in many cases. Some jurisdictions use proportionate-share agreements where the developer pays only for the portion of an improvement attributable to their project. In other cases, phased improvements, alternative access designs, or trip reduction measures can reduce the cost. A well-scoped TIA with realistic mitigation is less likely to produce this situation.

Most agencies require traffic counts collected within 12 months of the TIA submittal. Counts should be taken during typical conditions, not during school breaks, major holidays, or construction detours. Some jurisdictions have stricter requirements, and seasonal adjustment factors may be applied depending on the data collection period.

Policies vary by jurisdiction. Some agencies require a TIA update if the development has not broken ground within a certain period (often 2 to 5 years), if traffic conditions have changed significantly, or if the project scope changes. Check with your reviewing agency for their specific policy on TIA validity periods.

Agency reviewers may issue comments requesting additional analysis, different assumptions, or revised mitigation recommendations. This is a normal part of the review process. The traffic engineer responds to each comment, provides additional documentation if needed, and revises the report. Most TIAs go through at least one round of comment-response before approval.

A full TIA before acquisition is usually premature, but a preliminary traffic assessment or feasibility review can identify potential red flags, such as high-volume adjacent roads, limited access options, or proximity to failing intersections. This type of early review can inform the purchase decision and help avoid surprises during the entitlement process.

Trip generation is the process of estimating how many vehicle trips a development will produce during a given time period, typically the AM and PM peak hours. Estimates are based on the ITE Trip Generation Manual, which provides rates derived from traffic count studies at thousands of similar developments across the country. Trip generation is the starting point for every TIA.

Mitigation refers to the improvements or changes recommended to address the traffic impacts identified in the study. Examples include adding turn lanes, modifying signal timing, relocating driveways, improving pedestrian crossings, or adjusting internal site circulation. The goal is to bring traffic operations within acceptable levels as defined by the reviewing agency.

No. Most jurisdictions set thresholds based on trip generation, project size, or development type. Projects below the threshold typically do not require a full TIA, though a traffic memo, trip generation letter, or access study may still be needed depending on the jurisdiction and the specifics of the project.

Most TIAs fall in the $7,000–$25,000 range depending on project size and scope. Data collection (traffic counts and field measurements) typically adds $1,000–$5,000. The main cost drivers are the number of study intersections, analysis scenarios, special requirements like microsimulation, and whether the project involves multi-agency review. A clear scope agreed upon with the reviewing agency before starting helps avoid unexpected costs.