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From page 58... ... 58 Double Left-Turn Lane Field Study Background The objective of NCHRP Project 03-102 was to recommend improvements to the guidance provided in the AASHTO Policy on Geometric Design of Highways and Streets (commonly known as the Green Book) Read the entire page →
From page 59... ... 59 traffic. In constrained situations, 30-ft throat widths are acceptable minimums. Read the entire page →
From page 60... ... 60 on the order of 1870 pcphgpl" (75) Read the entire page →
From page 61... ... 61 Objective and Measures of Effectiveness The objective for this research study was to determine the effects of geometric characteristics on operations for double left-turn lanes. The following geometric variables were the focus of this study: receiving leg width, left-turn lane width, and downstream friction point (type and distance) Read the entire page →
From page 62... ... 62 characteristics of the sites. The goal was to collect data from sites that varied in the following characteristics: • Left-turn lane widths (range between 9 and 12 or more ft) Read the entire page →
From page 63... ... 63 Figure 5-1 depicts the site characteristics gathered by technicians for each site. The descriptions of the per-queue variables are provided in Table 5-6. Read the entire page →
From page 64... ... 64 • Camcorder #3 captured vehicles turning in the intersection and erratic vehicle maneuvers caused by the friction location. Camcorder #3 was placed about 20 ft after the friction location on the receiving leg (see Fig - ure 5-3) Read the entire page →
From page 65... ... 65 Figure 5-1. Graphic used to assist with gathering site characteristics. Read the entire page →
From page 66... ... 66 Figure 5-2. Example of video camera setup for double left-turn lanes study. Read the entire page →
From page 67... ... 67 To handle extreme outliers, researchers decided to use a maximum selected saturation-flow-rate value based on an assumed headway of 1 sec, which resulted in a maximum saturation flow rate of 3600 pcphgpl value. A total of 18 of 10,041 data points were removed (less than 0.2%) Read the entire page →
From page 68... ... 68 A variable was created to calculate the percent of the volume present within a cycle to each lane. This lane share variable is aimed at determining the proportion of vehicles that use a lane out of all left-turn vehicles recorded during a cycle. Read the entire page →
From page 69... ... 69 Analysis/Results Saturation Flow Rate Saturation flow rate represents the number of vehicles served by one lane over 1 hr of green time. It is calculated using the headway between following vehicles when all vehicles being considered were passenger cars and were present at the start of the green phase. Read the entire page →
From page 70... ... 70 a 3.4% decrease in saturation flow rate (-56/1680) , while two U-turning vehicles are associated with a 6.7% decrease in saturation flow rate (-113/1680) Read the entire page →
From page 71... ... 71 cant. The model results indicate that the addition of this new lane results in an increase in saturation flow rate of about 50 pcphgpl. Read the entire page →
From page 72... ... 72 saturation flow rate of the double left-turning traffic. While significant, the incremental difference is small. Read the entire page →
From page 73... ... 73 better focus on data when lane selection may be more influenced by geometric conditions, two datasets were created: • Dataset 11 contained the data when 11 or fewer vehicles are in each lane. • Dataset 7 included the cycles when at least one of the two lanes had seven or fewer vehicles. Read the entire page →
From page 74... ... 74 Site Dataset 11 Dataset 7 fLU L2 share Count fLU L2 share Count AZ-FS-03 84% 0.58 76 81% 0.60 64 AZ-FS-04 88% 0.51 171 87% 0.51 146 AZ-FS-05 90% 0.52 92 88% 0.52 69 AZ-FS-06 86% 0.58 213 85% 0.58 192 AZ-FS-07 85% 0.57 23 85% 0.57 23 AZ-PH-02 87% 0.55 93 87% 0.55 92 AZ-PH-06 92% 0.50 64 92% 0.50 64 AZ-PH-07 93% 0.51 36 92% 0.51 25 AZ-PH-08 90% 0.55 35 90% 0.55 35 AZ-PH-09 93% 0.48 32 93% 0.48 32 AZ-PH-12 87% 0.44 127 86% 0.43 116 AZ-PH-13 93% 0.47 69 91% 0.46 25 AZ-PH-15 93% 0.48 101 90% 0.47 62 AZ-PH-16 95% 0.48 23 91% 0.46 7 AZ-TU-09 91% 0.49 81 91% 0.49 68 AZ-TU-10 91% 0.47 85 89% 0.46 58 CA-BA-04 92% 0.53 14 92% 0.53 14 CA-ST-01 91% 0.54 24 86% 0.58 10 CA-ST-02 91% 0.52 73 88% 0.53 52 CA-ST-04 91% 0.52 40 91% 0.52 37 TX-CS-01 91% 0.50 86 91% 0.51 82 TX-CS-02 89% 0.51 77 87% 0.51 63 TX-CS-03 93% 0.49 62 92% 0.49 54 TX-CS-04 92% 0.53 102 90% 0.54 69 TX-HO-02 90% 0.54 150 89% 0.55 115 TX-HO-03 89% 0.47 84 89% 0.47 83 Total 90% 0.51 2033 88% 0.52 1657 Table 5-13. Average lane utilization factor and L2 share per site. Read the entire page →
From page 75... ... 75 left-turn lane group. Note, however, that the dataset does not include information on whether there was activity at the friction point during a cycle. Read the entire page →
From page 76... ... 76 the intersection. Several other study sites also had a driveway or intersection near the intersection but did not have as many driver behaviors. Read the entire page →

From page 58...

... 58 Double Left-Turn Lane Field Study Background The objective of NCHRP Project 03-102 was to recommend improvements to the guidance provided in the AASHTO Policy on Geometric Design of Highways and Streets (commonly known as the Green Book)