Traffic Impact Analysis

A study that evaluates how a proposed development project will affect traffic conditions on surrounding roads and intersections, often required as part of the permitting or environmental review process.

What Is a Traffic Impact Analysis?

A traffic impact analysis (TIA) is a technical study that evaluates the transportation effects of a proposed development project. It measures existing traffic conditions, projects how the new development will change those conditions, and recommends improvements (called mitigations) to maintain acceptable levels of service on surrounding roads and intersections. TIAs are typically prepared by licensed traffic engineers and submitted to the local jurisdiction as part of the project approval process.

When Is a TIA Required?

Most jurisdictions set trip-generation thresholds that trigger the requirement for a TIA. Common thresholds range from 50 to 100 new peak-hour vehicle trips, though this varies by location. Projects that typically require a TIA include shopping centers, office buildings, large residential developments, hospitals, schools, and industrial warehouses. Some jurisdictions require a preliminary traffic memo for smaller projects that fall just below the full TIA threshold.

What a TIA Includes

A typical TIA covers existing traffic counts and intersection levels of service, trip generation estimates using ITE Trip Generation Manual rates, trip distribution and assignment to the street network, future baseline traffic projections (with and without the project), intersection and roadway capacity analysis, sight distance evaluation, access and circulation design, pedestrian and bicycle accommodation, transit access, and recommended mitigation measures such as traffic signals, turn lanes, street widening, or transportation demand management programs.

Typical Timeline

A traffic impact analysis typically takes 4 to 12 weeks to complete, depending on the number of intersections studied, data collection needs, and agency review requirements. Data collection (traffic counts) often takes 1-2 weeks. The analysis and report preparation takes 2-6 weeks. Agency review and comments add another 2-4 weeks. Revisions after agency feedback may add additional time. In congested urban areas or for very large projects, the process can extend to 4-6 months.