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Interchange Studies
Interchange Studies

Control of access on the Interstate and other freeway systems is considered critical to providing the highest quality of service in terms of safety and mobility. Sometimes referred to as an Access Point Request, these studies are needed on Interstate and other freeway systems in accordance to Federal Code 23 U.S.C. 111 and FHWA Policy - Additional Interchanges to the Interstate System (Federal Register: February 11, 1998, Volume 63, Number 28).

The documentation required depends on the type of change requested - new or revised.

  • New Access is the addition of a point of access where none previously existed. This includes the construction of an entirely new interchange such that it will result in additional points of access or additional ramps to existing interchanges. As an example, the reconstruction of an existing diamond interchange to a full cloverleaf interchange would add four new points of access.
  • Revised Access is the revision of existing ramps or crossroads within the limited access area such that the number of access points will remain the same but the operation and/or safety of the Interstate/freeway system may be affected. The changing of a cloverleaf interchange to a fully directional interchange, the adding of turn lanes at crossroad-ramp intersections, the adding of through lanes on the crossroad through an interchange, or the widening of a single lane entrance ramp to two lanes are considered examples of revised points of access.

New or revised access point requests require the preparation and processing of an Access Point Request Document. Generally, new access requires an Interchange Justification Study (IJS), and revised access requires either an Interchange Modification Study (IMS) or an Interchange Operations Study (IOS). Ultimately, the study is going to demonstrate that the modification to the Interstate will not degrades its capacity or safety.

Interchange Operations Study (IOS) Guidance

Projects that require an Interchange Operations Study (IOS) include:

  • Changing lane configurations at a ramp intersection approach, including:
  1. Adding a left or right turn lane along the crossroad
  2. Adding a thru lane on the crossroad
  3. Adding turn lanes to the exit ramp
  4. Changing lane assignments without altering the number of lanes
    1. Example: Changing a 2-lane approach from (Left / Thru-Right) to (Left-Thru / Right)
  5. Implementing a Road Diet – reducing the number of lanes on the crossroad
  6. “Squaring” up a continuous right turn lane from the ramp/crossroad and putting it thru the signal
  • Changing the exit or entrance ramp terminus point with the mainline by:
  1. Creating an optional exit lane
  2. Creating a 2-lane exit
  3. Creating a 2-lane entrance
  • Shifting a ramp’s location within the same interchange configuration without changing the ramp type
  • Changing traffic control type at the ramp/crossroad intersection:
  1. Example: Revising from signalized/unsignalized condition to a roundabout
  • Adding an auxiliary lane between two adjacent interchange ramps (preferably less than 1 mile) where the single auxiliary lane does not function as a mainline travel lane
  • Altering access between managed lanes and general purpose lanes on the Interstate

For all other modifications to the interchange or mainline that result in significant changes to the operations that are not covered above and do not warrant an Interchange Modification Study, please contact the Office of Roadway Engineering.

See Additional Guidance and Sample Report

Prequalification

There is a prequalification requirement for consultants who want to prepare interchange justification studies (IJS), interchange modification studies (IMS), or interchange operations studies (IOS). For more information, visit the Office of Consultant Services or Traffic Academy.

Traffic Academy Webinars - 2020

Session 1

Session 2

Traffic Academy - Interchange Studies Slides (2020)