What is a Traffic Impact Study?

What is a Traffic Impact Study?

A traffic impact study (TIS) or also called a traffic impact analysis (TIA) is a document prepared by qualified traffic engineering firms to assess the potential effects of a proposed development on the surrounding roadway network.  Typically conducted by traffic engineers, a TIA forecasts the additional traffic associated with a proposed development, identifies potential problems that might influence traffic flow, and suggests ways to mitigate any negative effects.


The purpose of a TIS is to determine the potential traffic impacts of a proposed development on the existing road system. It helps ensure safe and reasonable traffic conditions once the development is complete and protects the community’s investment in its street system. The study may also recommend geometric or operational roadway improvements to accommodate the increased traffic.


A TIS or TIA takes into account factors such as trip generation, traffic volume, intersection capacity analysis, infrastructure adequacy, and the overall impact on traffic patterns in the vicinity of the proposed development. The study is conducted based on specific guidelines and procedures to ensure consistency and accuracy of information regarding the traffic impacts of the development.


These studies are essential for developers, city planners, and transportation agencies to make informed decisions about the potential impacts of a development and to implement necessary measures to mitigate any negative effects on the transportation system.

Special Note

Please note that the specific requirements and regulations for conducting TIS or TIA may vary based on the jurisdiction or country. consulting the relevant local authority’s guidelines or seeking professional advice is recommended.

Why do I need a traffic impact study?

Local governments – towns, cities, counties, and states – have a responsibility to ensure public health, safety, and welfare. For new development, redevelopment, and rezoning projects, these responsibilities are managed through various planning and engineering review processes, including the review of the potential “traffic impacts”. Because new developments typically “generate” additional vehicle trips that use will use public roads, a traffic impact study, commonly referred to as a TIS or TIA, is used to help determine the extent of these impacts. In general, a traffic impact study provides a review of:

  • Existing conditions
  • The proposed development, site access, and circulation
  • Effects of new trips on roadways and intersections

How do I know if my development will need a traffic impact study?

Local governments typically require a TIS when a new development is expected to generate 100 or more new trips in the peak hour once it is fully constructed and open. These calculations are based on the Institue of Transprotation Engineers (ITE) Trip Generation Manual. The manual includes trip calculations for dozens of land use types.

If a development is expected to generate less than 100 peak hour trips it may not need a TIS; however, many local governements will require a simple summary letter, sometimes called a traffic statement.

If you are in the project planning phase, we can help you determine whether you need a traffic impact study:

  1. Our traffic engineering team offers free consultations to discuss your development’s needs. Call us at (602) 499-1339 or email us.
  2. If you manage many different types of development projects, we have created a summary sheet that includes approximate development sizes that meet the 100 peak hour trip thresholds for some of the most common land uses that we see. This sheet is greatly simplified, as there are many ways to analyze site trips generation. Please email us to request a copy. If your particular development type is not included in the list, please give us a call to discuss.

Is a traffic impact study the same as a traffic impact analysis?

Traffic Impact Studies are known by many names. Depending on the reviewing agency and what is being developed, these terms can vary along with the level of effort required to develop the study. The most common names you will see include:

  • Traffic Study
  • Traffic Statement/Traffic Impact Statement
  • Traffic Impact Study (TIS)
  • Traffic Impact Analysis (TIA)
  • Traffic Impact & Mitigation Analysis (TIMA)
  • Traffic Operations Analysis (TOA)

Who prepares a traffic impact study?

Traffic impact studies are prepared by qualified consultant traffic engineers. Many agencies prefer that a TIS be completed by someone that is also certified as a Professional Traffic Operations Engineer (PTOE). In some cases, the local government serves as an intermediary to arrange for a consultant to perform the development’s TIS; however, this is not a common practice.

How long does it take to complete a traffic impact study?

The schedule for completing a traffic study can range from a few days to 6 weeks or longer. There are several factors that influence the schedule for completing traffic impact studies. A few of the primary factors include:

  • Agency coordination on scope: Obtaining agency buyoff on scope before the study is started is a best practice. It does take some extra time up front, but typically reduces rework and saves time in the long run.
  • Development size: Larger developments require more intersections to be studied
  • Development complexity: Phased developments require significantly more effort to analyze
  • Ability to collect counts: Holidays, special events, local school schedule, and weather can affect when counts can be taken.

What does it cost to complete a traffic impact study?

Unfortunately, there are no typical costs for a TIS, as each site is unique based on the scope of the project. The minimum cost threshold is typically a couple thousand dollars. In addition, once the TIS is initiated, changes to land use size, type, and location; site access; circulation, can lead to additional costs associated with rework.

My development reviewer is requiring a TIS, now what?

Your very next step is to request a proposal from a qualified traffic engineering consultant. Greenlight Traffic Engineering specializes in preparing traffic impact studies for developments of all types and sizes. Greenlight knows that speed and responsive service are crucial when it comes to private development. We have helped developers, zoning attorneys, architects, and engineers get their project approved quickly.

If you would like to request a proposal from us, please fill out our contact form, or reach out at (602) 499-1339 or email us.