An Evaluation of Turning Movement Counts and Estimation of Initial Turning Proportions

Abstract

An analysis on the impact of traffic is required before transportation designs can be performed. This impact analysis is even further supported with a shift towards creating more environmentally sustainable designs. Turning movement volumes are an important variable in traffic impact analysis. They provide the basic input needed in various transportation processes including traffic studies, forecasting, analysis, and determining the operational performance of an intersection. In an urban planning setting, turning movement counts provide the variable needed to properly utilize the four-step modeling process that generates the flow of vehicles in a network. Manual counting of turning vehicles is the most common practice to obtain turning movement volumes, however, this can be an expensive and exhaustive task. This research provides an evaluation of existing turning movement counts at various intersections in College Station, Texas. Initial turning movement proportion ranges are estimated using definable roadway characteristics, such as lane group and functional classification. These proportions and the intersection approach volumes/AADT are then used to estimate turning movement volumes for the intersection with Hauer’s algorithm and a basic proportion distribution method. The accuracy of each turning movement volume estimation is analyzed for the different turning proportions and compared to observing turning movement volumes. Finally, a recommendation is proposed for the range of turning movement proportions to estimate turning movement volumes.