Mindy Wallace, the Planning Review Supervisor at the Ada County Highway District (ACHD), provided an in-depth overview of the traffic impact study process during a recent government meeting. The discussion highlighted the importance of these studies in assessing the potential effects of new developments on local traffic patterns.

Wallace explained that a traffic impact study is typically required for developments expected to generate 100 or more new trips during the evening peak hour. However, other agencies, such as the Idaho Transportation Department (ITD) and local land use agencies, may also mandate these studies based on specific circumstances. The process begins with determining the need for a study, followed by the applicant's consultant developing a scope of work, which is then reviewed and approved by ACHD.

The analysis conducted in these studies includes existing conditions, background traffic, and cumulative impacts to assess whether intersections and roadways will meet ACHD's acceptable level of service thresholds. If the thresholds are exceeded, Wallace noted that the response varies based on the situation. For instance, if a roadway is already congested but programmed for improvements, ACHD may allow the development to proceed while acknowledging the increased congestion.

Commissioners raised concerns about whether traffic studies conducted by consultants hired by applicants could be biased. Wallace acknowledged this concern, stating that while applicants choose their consultants, ACHD reviews the studies to ensure they meet technical standards. John Wasson from ACHD added that multiple groups within the agency review these studies, and inadequate plans can be rejected and sent back for revision.

The meeting underscored the balancing act faced by ACHD and local agencies in managing development while addressing traffic congestion and ensuring public safety. As development continues to increase in the region, the effectiveness and reliability of traffic impact studies will remain a critical focus for local planners and decision-makers.