Estimating Intersection Turning Movements

About the report:

Turning movement (TM) counts are used for a variety of intersection analyses, including traffic operations analyses, intersection design, and transportation planning applications. For many planning and design applications, especially in the case of proposed future improvements to an intersection or even proposed new intersections, future year TM counts are needed for the analysis. Accordingly, there is a need to forecast turning movements at the intersection. The purpose of the research was to inventory and review the methods used to forecast intersection turning movements. The effort was limited to a literature review and a limited survey of practitioners to determine methods currently being used to make such forecasts. Based on this limited review, it was found that the state-of-the-practice for estimating turning movements is based on using growth factors to project link volumes and TM counts. In many cases, engineering judgment is used to account for special conditions or to accommodate known or anticipated land use changes that may significantly impact turning movements. The implication, therefore, is that although there are similarities among methods used by a variety of organizations for a variety of purposes, there is no identifiable preferred means of estimating turning movements. The most definitive technique found is the procedures described in the National Cooperative Highway Research Project (NCHRP) Report 255.

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