No abstract

No abstract

No abstract

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.

The increase in truck traffic on interstate freeways continues to raise concerns about the large trucks’ dimensions that cause sight distance problems and about trucks’ low capability to accelerate, decelerate, and maintain speed particularly on steep grades. To address safety and operational concerns caused by truck traffic, a multitude of restriction policies have been instituted around the United States. This study was aimed at determining the operational and safety impacts of the 24-h restriction of trucks from using the median lane of a six-lane freeway corridor, Interstate 75 in Florida. It should be noted that traffic flow on this corridor is relatively uncongested and the corridor operates at Level of Service B or better throughout the day. Analysis of field and simulation data indicated that the difference between truck and passenger car speeds and travel times were insignificant on the unrestricted middle and shoulder lanes. About two-thirds of both passenger cars and trucks were traveling within the 10-mph pace that ranged from 70 to 80 mph in the corridor, which has a speed limit posted at 70 mph. The field data also indicated that trucks were able to use the middle lane to pass 25% of the time during the truck peak-hour period with the assumption of a 10-s gap acceptance. In addition, simulation analysis indicated that opening all lanes to trucks increased the number of lane-changing maneuvers by 11% in the daytime, a phenomenon likely to increase crashes in the corridor.