SATURATION FLOWS OF EXCLUSIVE DOUBLE LEFT-TURN LANES

The objectives of this study were to develop estimates of the saturation flows of exclusive double left-turn lanes, and to investigate the physical and operating characteristics of the intersection that may affect left-turn saturation flows. The results are based on observations of 3,458 completed left turns from exclusive double left-turn lanes on 14 intersection approaches in Austin, College Station, and Houston, Texas. Based on the results of this study and a review of the data from a limited number of related studies, an average double left-turn saturation flow rate of approximately 1,600 vehicles per hour of green per lane would appear to be a reasonable value for most planning applications. This flow rate can be assumed to be achieved for the third vehicle in the queue and beyond. Also, this flow rate appears to be applicable for mixed traffic conditions in which heavy vehicles constitute as much as 3 to 5 percent of the left-turn traffic volume.