Estimation of Left‐Turn Traffic Parameters

The capacity of exclusive left‐turn lanes and the passenger car equivalent of left‐turn vehicles are two parameters commonly used for the planning, design, and operation of signalized intersections. Existing methods for estimating the two parameters, however, may not have adequately accounted for the effects of signal settings and the presence of multiple opposing lanes. This study examines whether such effects are significant enough to warrant modifications of existing models. It analyzes relationships of the left‐turn movement to signal settings and the presence of one and two opposing lanes on the basis of existing understanding and computer simulation. In estimating the leftturn lane capacity, the study reveals that the use of a single formula regardless of the number of opposing lanes could lead to significant errors. It also shows that signal settings and the number of opposing lanes should be treated explicitly in estimating the passenger car equivalent.