Combined Approach for Determining Turning Movements at T-Junctions with U-Turns

Presented in this study is a combined approach for determining turning movements at traffically indeterminate T-junctions with U-turns. This approach combines the use of turning movement counts for the three redundant turning movements together with a mathematical model to be developed that relies on link counts and a volume count at a chosen section within the intersection. The model consists of a consistent system of six linearly independent algebraic equations in nine unknowns. The paper shows that the use of an internal section for volume count inside the junction is required for the system of equations to be linearly independent. For each chosen internal section within the junction, the Gaussian elimination process on the system of equations shows that there is a certain traffic stream (turning movement) that can be determined directly as it is independent of the three redundant traffic streams. The choice of the three redundant turning movements, determined manually or by video-camera, is subjected to some restrictions depending on the internal section used. The choice of all three Uturns as the redundant turning movements is always correct and possible. The paper reveals also that other combinations of three redundant turning movements, are also possible. Such a combination represented by two right-turning movements with a U-turn, was applied successfully. The application of the developed approach on a T-junction with U-turns and known O-D matrix validated this economic approach. One case study for a T-junction utilizing traffic data collected from the urban area of a city in Iraq, are set up to demonstrate the application of the proposed combined approach. The traffic data was collected both manually and by automatic traffic counters. Before using the automatic counts in the developed approach, they were corrected for undercounting and inconsistency of in- and outflows. The estimated turning movements using the developed approach are in good agreement with those obtained manually indicating the reliability of the developed approach for T-junctions with U-turns.