Best planning and implementation toolbox

Traffic Impact Assessment:

Purpose of Tool:
The purpose of Traffic Impact Assessment (TIA) is to establish uniform guidelines for conducting studies to analyze the potential transportation impacts resulting from the construction of a new development, or from redevelopment of an existing property. TIAs are used to identify potential issues, such as safety, congestion, and access that may arise from the construction of a new or expanded development, as well as determining the necessary improvements to mitigate those impacts. Some local TIA programs may also include a cost sharing analysis element that identifies the portion of the mitigation costs to be borne by the developer versus that of the jurisdiction that owns and maintains the impacted transportation facilities.

Benefits of Using Tool:
The benefits of TIAs include helping communities to:
  • Assess the potential impacts of new development or redevelopment
  • Understand additional traffic forecasts associated with new development (or redevelopment),
  • Determine the transportation improvements that are necessary to mitigate potential impacts from the new development or redevelopment
  • Make land use decisions
  • Allocate resources in an equitable manner
  • Assist developers in understanding potential risks and investments in transportation improvements
  • Ensure safe travel conditions on the transportation system subsequent to construction
  • Minimize the negative impacts created by developments by helping to ensure that the transportation system can accommodate the new development or redevelopment
  • Provide direction to decision makers
  • Protect the community investment in the existing transportation system

    Steps Involved to Use Tool:
    The basic four steps involved with completion of a TIA are as follows:
  • Step 1: Identify of extent of study area, years of analysis, assumptions and methodology
  • Step 2: Data Collection including traffic counts and field assessment
  • Step 3: Analyze existing and future conditions including capacity of key intersections and roadway segments, as well as potential safety, land access, and multimodal issues
  • Step 4: Determine mitigation measures to address future deficiencies identified. This step also includes the development of recommendations, which may include details including responsible parties, costs, phasing and required institutional action items.

    Special Requirements to Use Tool:
    In many communities, traffic impact assessments are a standard part of the development review process. Thresholds that trigger a TIA process and quality of service or level of service standards are often established by ordinance. For example, the Institute of Traffic Engineers (ITE) recommends traffic impact studies for any development generating more than 100 new daily trips, or for developments that are located in sensitive areas with respect to transportation system operations or safety. Local governments will need to establish a standard TIA process for the development community which may include thresholds for developments that require TIAs, study area boundaries, standards for performance of the transportation system with the forecast traffic from developments, and required fees or mitigation measures associated with impacts on the transportation system.

    Specials Resources Needed to Use Tool:
    Resources may be necessary to collect or develop the information for conducting TIAs. This information includes a quantitative description of proposed development (or redevelopment) projects, historic and current traffic data, safety/crash data, traffic operational information (such as signal timing plans), and information on planned and programmed transportation projects. Much of the data needed may be available from the local departments of public works, transportation departments, Metropolitan Planning Organizations, and/or state Departments of Transportation. Staff time to forecast future traffic within the study area, review programmed improvements, and review TIA studies provided by developers may be necessary, depending on the TIA requirements.

    Communities / Agencies that Have Used Tool:
    Many local jurisdictions in Texas require traffic impact analysis. In the Greater Houston Region, a TIA is required in the cities of Pearland, Missouri City, Sugar Land, and Harris County. Other cities in Texas such as Round Rock, Grand Prairie, Plano, Arlington, Fort Worth, El Paso, Austin, and San Antonio require TIAs. Two specific examples are:
  • City of Fort Worth, Texas: The City’s 2008 Development Guide specifies traffic impact assessment requirements and associated impact fees.  Contact:

    City of Fort Worth
    Director of Planning and Development
    City Hall, Lower Level
    1000 Throckmorton St.
    Fort Worth, TX 76102

    City of Fort Worth Transportation Impact Fee Manager

  • Pinal County, Arizona: Pinal County established TIA guidelines in 2007.  Contact:

    Pinal County
    Public Works
    P.O. Box 727
    Florence, AZ 85232

    Metrics to Use to Monitor Tool Effectiveness:
    TIAs are used to project the current and future traffic impact that a development may have on a particular area. Measures of effectiveness may include roadway level of service, as well as multimodal level of service maintained after developments occur. A case study was completed in Eugene, Oregon for Barger Crossing Shopping Center, which was built in 1996, to determine the accuracy of the original TIA. The study found that the original TIA under-predicted the number of peak hour trips in 2007 by 57%.

    List of Resources to Obtain Additional Info:
  • Best Practices for Traffic Impact Studies, sponsored by FHWA and Oregon DOT, 2006
  • City of Houston Traffic Impact Assessment Guidelines
  • Pinal County Traffic Impact Assessment, Guidelines and Procedures, January 2007
  • Community Guide to Development Impact Analysis by Mary Edwards
  • City of Fort Worth Transportation Impact Fee information
  • City of Fort Worth Development Guide
  • Institute of Transportation Engineers reference materials on trip generation rates