Site Characteristics Affecting Operation of Triple Left-Turn Lanes

The growth of traffic flow in urban areas has resulted in increased installation of triple left-turn lanes with the aim of reducing vehicle delays, queue lengths, and vehicle storage bay lengths by dividing the left-turn queue demand among three lanes. The study reported here analyzed the influence of a number of geometric factors found at 15 triple left-turn lane sites in Florida on saturation flow, lane usage, and lane utilization. A total of 2,395 lane cycles and 38,023 vehicles were observed. The observed saturation flows yielded a mean saturation flow of 1,859 passenger cars per hour of green per lane (pc/h/ln) with the 95% confidence interval of 1,810 pc/h/ln to 1,907 pc/h/ln. The Fisher least significant difference test and the Hsu multiple comparison with the best test were used to determine the statistical significance of the variables’ influence on saturation flows. The results showed that triple left-turn lanes on downgrades and with an angle of turn less than 90 degrees were the two characteristics that most contributed to high saturation flow, and triple left-turn lanes located on oneway streets and on curved approaches had the lowest saturation flow. Lane utilization was dependent on the geometrics of the intersections: shadowed left-turn lanes had lower utilization of the innermost lane compared with unshadowed lanes.