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The What and Why of TIA

20 December 2019

Thomas Duncan, PE, PTOE, discusses key points concerning traffic impact analysis.


You’ve met with the local municipality and they are requiring a TIA for your proposed development. So, you are now faced with two main questions: what is a TIA and why do you need one?

What is a TIA?

A TIA, or Traffic Impact Analysis, is a study of how your development will affect the surrounding roadways and their traffic patterns. Every development will “generate” vehicle trips, meaning people will want to travel to and from your new development. A TIA determines where those expected trips will circulate and how the roadways and intersections around your development will be affected.

TIAs are typically required by municipalities during their permitting process and every municipality has their own requirements. Many cities and counties have a published design criteria manual to guide in the development of the study.

Why Do I Need One?

There are really two answers to this question:

  • Because the municipality typically will not permit construction activities without it.
  • To ensure that your target customer can efficiently access your site. (Traffic congestion around a development can deter patrons from visiting your new investment.

What’s in a TIA?

A Traffic Impact Analysis typically contains the following items:

  • Size and type of development being proposed
  • Number of phases and proposed completion years for construction
  • Study area roadways and intersections
  • Locations of site driveways
  • Internal traffic operations including valet, ride share, shuttles, emergency vehicles, parking, pedestrian walkways, bike path connections, etc.
  • Other development studies within the area
  • Expected traffic growth

Not One Size Fits All

TIAs, like all developments, come in a variety of sizes and costs. Development projects that are forecasted to generate little traffic will typically require a form or letter to the agency, while larger sites could require a very large and complicated study. Different types of development also generate different types of traffic. Warehouses per square foot will generate fewer vehicle trips than commercial properties; however, those trips will contain more large trucks. At Walter P Moore, we have a variety of multi-modal experts that can help you navigate the ins and outs of TIAs.

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