Traffic Impact Analysis (TIA)

A Traffic Impact Analysis (TIA) study is performed to assess how a new development will affect the surrounding transportation network. Based on this impact, mitigation options are evaluated and selected.

Subsequently, the new development's proportional share of the cost for each improvement element (known as the pro-rata share) is determined. The final TIA report includes all findings and recommendations and is submitted to the authorities for the permitting process.

The most commonly used methodology for conducting a TIA is from the Institute of Transportation Engineers (ITE). With this method, existing traffic counts are collected for both morning and afternoon peak hour. The total trips generated by the new development during these peak hours are calculated using the ITE's Trip Generation Manual and/or local manuals. These generated trips are then categorized as pass-by, diverted, or added traffic.

Pass-by traffic is a portion of the development's demand that already exists as part of the traffic on the road with direct access to the site. Once the development is built, this pass-by traffic will simply make a stop along its original route. Diverted traffic is a share of the development's demand that is already within the study area. After the development is built, this diverted traffic alters its original route to visit the new development. The turning movements at intersections are adjusted to account for these two trip categories.

The added traffic is allocated (distributed) to where it enters or exits the network (network access points). The traffic demand between the development and each of these access points is then assigned to feasible routes.

This process allows for the determination of the total volume of each turning movement, which is then analyzed using traffic operations analysis and warrants analysis methods to recommend mitigations and calculate pro-rata shares.

In addition to evaluating traffic impacts, a crucial element for new developments is the parking requirements analysis. This distinct analysis, often performed alongside the TIA, determines the necessary parking supply to support proposed land uses, ensuring compliance with local zoning ordinances and providing adequate space for the development.