First things first: What is a Traffic Impact Study?

A traffic impact study (TIS) or a traffic impact analysis (TIA) is a document prepared by qualified traffic engineering firms that assess the potential effects of a proposed development on the surrounding roadway network.

The study is conducted to ensure that the proposed development will not cause undue impacts to the transportation system and to identify any necessary mitigation measures to alleviate those impacts.  In some cases, a TIS may also be used to assess the potential impacts of an existing development that is experiencing significant changes in traffic patterns.

A traffic impact study will typically consider factors such as:

  • traffic volume
  • vehicle mix
  • speed
  • turning movements
  • possible pedestrian and bicycle activity

Once completed, the TIS can be used to help inform decisions related to zoning, land use, and transportation infrastructure investments.

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 TIS?

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 TIS?

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 TIS?

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 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 reach out at (602) 499-1339 or email us.