What Should the Scope of a Traffic Study Be (Part 1 of 2)?

By Mike Spack, PE, PTOE

This is a big question because the scope of the study will lead to the physical mitigation measures the developer will be responsible for. Scoping a traffic study is typically based on the size of the development and the type of location it is going into.  On a small development, the developer might be required to add a turn lane at the main driveway. For a regional shopping mall, the developer might be required to build a freeway interchange a mile away. If there aren’t feasible mitigation measures, the responsible government agency may require a less dense development or a phasing plan that is dependent on public infrastructure improvements.

There are two key components to the traffic study.  This post focuses on how far away from the development the study area needs to address.  A follow-up post (Part 2) will address how far into the future we need to analyze. The image at the left is an example of a Spack Consulting traffic study proposal which includes the core elements that we include when working with a client.

The Institute of Transportation Engineers (aka ITE) has developed a Recommended Practice titled Transportation Impact Analyses for Site Development.  It details the study area limits that should be used for different size developments. The following list presents ITE’s guidelines.  You can use this as a starting point to make sure your traffic study has the proper scope.

• Fast Food Restaurant – Adjacent intersection if corner location
• Service Station (with or without fast food counter) – Adjacent intersection if corner location
• Mini-mart or convenience grocery with or without gas pumps – 660 feet from access drive
• Other development with fewer than 200 trips during any peak hour – 1,000 feet from access drive
• Shopping center less than 70,000 sq. ft. OR a development with 200 to 500 peak hour trips – All signalized intersections and access drives within 0.5 miles from a property line of the site and all major unsignalized intersections and access drives within 0.25 miles
• Shopping center between 70,000 sq. ft. and 100,000 sq. ft. OR an office or industrial park with 300 to 500 employees OR a well-balanced, mixed use development with more than 500 peak hour trips – All signalized and major unsignalized intersections and freeway ramps within 1 mile of a property line of the site
• Shopping center with more than 100,000 sq. ft. OR an office or industrial park with more than 500 employees OR any other development with more than 500 peak hour trips – All signalized intersections and freeway ramps within 2 miles of a property line, and all major unsignalized access (streets and driveways) within 1 mile of a property line of the site
• Transit Station – 0.5-mile radius

Please note this is a starting point for scoping out a traffic impact study.  Coordinate with the jurisdictions involved in reviewing your traffic study as there may be local standards that are different than ITE’s guidelines.