New development sites can impact the surrounding roadway system by adding to existing traffic volumes or altering traffic patterns. In addition to designing appropriate access for proposed developments, planners and developers should strive to maintain a satisfactory level of transportation service and safety for all roadway users.
Traffic access and impact studies gather and analyze information that will help determine the need for any improvements to interior, adjacent, and nearby road systems. Not all development proposals require a traffic access and impact study, but many do. Developers must contact MPC to ascertain their standing. Early in the development process, prior to the actual submission of plans, the applicant should conduct a preliminary trip generation assessment of any proposed Subdivision Concept Plan, Use on Review, or Development Plan to determine if a traffic study will be required. A 24-hour trip generation assessment showing 750 or more trips warrants a study.
The Applicant's Responsibilities
There are three levels of study, each based on the number of trips generated in a 24-hour period. ADT or Average Daily Trips is the term used to refer to this number. The applicant should contact MPC staff before beginning the study to confirm the level and requirements of the study.
Level I (750 - 3000 ADT) Each access point the development will have to an existing roadway (including public roads, joint permanent easements, and private driveways) is analyzed. Level I study is commonly required for larger residential subdivisions, office developments, and smaller commercial developments.
Level II (3000 - 6000 ADT) Each access the development has to an existing roadway is analyzed. In addition, the first control point beyond each access point is also studied. Control points are intersections controlled by traffic signals or stop signs. For cases where a traffic control device does not exist, MPC staff will determine the extent of the study. If a freeway interchange is near the property to be developed and is not signalized, MPC staff will determine if the ramps need to be included in the study. This level of study is commonly required for moderately sized commercial developments and larger office complexes.
Level III (More than 6000 ADT) Level III studies are complete traffic access and impact studies that analyze access points, the first control point beyond each access point, and other key intersections that will be affected by the proposed development. The exact area to be studied will be determined by MPC with input from the study preparer. Level III studies are usually warranted only with very large mixed-used and commercial developments.
Consult Appendix B of MPC's Administrative Rules and Procedures for details regarding required qualifications for study preparers, and for requirements pertaining to study content and format.