Lankershim Data Base Analysis - Clearing Queue Characteristics: An Initial Study
This page has the results of an initial study of the characteristics of the queues clearing on the northbound direction at intersection 2.

The first task was to identify from the complete data set, those vehicles that traveled northbound on Lankershim, at intersection 2.  The following table lists the vehicles, by lane, that travel through the intersection.  Each line represents the group of vehicles that travel through the intersection during a given cycle.  The number is the parenthesis at the end of each line is the number of vehicles in that group.

Lane 1 Lane2 Lane 3
86 87 90 144 154 192 194 208 (8)

235 239 254 266 270 272 296 319 (8)

335 358 392 411 455 480 482 (7)

497 515 556 591 (4)

629 682 (2)

769 790 826 831 890 (5)

893 (1)

902 917 922 933 956 968 984 1,007 1,009 (9)

1023 (1)

1,042 1,046 1,055 1,056 1,059 1,102 1,106 1,109 1,130 (9)

1,179 1,219 1,234 1,236 1,253 1,260 (6)

1,293 1,300 1,321 1,327 1,346 1,347 1,402  (7)

1,414 (1)

 64 74 (2)

76 85 92 186 188  (5)

213 215 242 245 247 267 269 273 (8)

368 393 396 400 409 441 445 461 466 473 478 484 486 490 (14)

494 1,429 581 603 (4)

617 618 641 662 665 670 681 732 754 760 768 (11)

776 781 782 788 789 801 809 811 817 849 882 (11)

886 896 906 937 948 953 967 973 (8)

1,018 1,024 1,048 1,057 1,071 1,086 1,092 1,122 1,134 (9)

1,157 1,205 1,220 1,221 1,246 1,255 1,261 1,269 1,270 (9)

1,287 1,296 1,299 1,311 1,326 1,328 1,341 1,370 1,378 1,392 1,395 1,398 1,406 1,411 (14)

1,417 1,421 1,438 (3)

 63 65 (2)

84 95 100 142 184 155 162 209 211 (9)

214 216 219 221 231 236 257 258 275 281 325 (11)

336 341 365 375 377 381 394 410 430 502 (10)

513 519 535 542 547 548 1,430 560 568 605 610 (11)

613 614 637 652 659 668 675 683 701 709 716 723 741 765 (14)

775 777 780 783 788 791 807 810 814 820 823 841 843 848 874 887 (16)

898 (1)

898 897 901 905 907 909 918 919 923 934 940 942 960 (13)

1,003 1,010 1,017 1,026 1,045 1,053 1,062 1,103 1,119 1,123 1,166 1,168 1,176 1,192 1,217 1,435 1,259 1,266 1,272 1,276 1,284 (21)

1,286 1,289 1,297 1,315 1,322 1,324 1,329 1,335 1,357 1,364 1,387 1,407 (12)

1,412 1,418 (2)

The following table summarizes the number of vehicles for each of the groups by lane:

Lane 1 Lane 2 Lane3
Group Number Group Number Group Number
1
2
3
4
5
6
7
8
9
10
11
12
13		 8
8
7
4
2
5
1
9
1
9
6
7
1		 1
2
3
4
5
6
7
8
9
10
11
12
 		 2
5
8
14
4
11
11
8
9
9
14
3		 1
2
3
4
5
6
7
8
9
10
11
12		 2
9
11
10
11
14
16
1
13
21
12
2

Lane 1, Group 1
The trajectory data for the first group of vehicles in lane 1 (86 87 90 144 154 192 194 208) were studied to determine the variation in headways for various distances upstream from the stop bar at intersection 2.  The chart  below shows the first four vehicles as they wait for the green (denoted by the horizontal line in the time-space diagram) and as they begin to move at the beginning of green, and the following four vehicles that arrive after the beginning of green.  The headways in ten foot increments, from LocalY = 350 to LocalY = 250, were studied.  The plot below shows the results.  From this plot, we can see that four vehicles stopped (beginning with vehicle 86 at LocalY = 346), one vehicle was slowed but did not stop, and three vehicles were not delayed at all.

The chart below shows the headways between vehicles at ten foot increments, beginning near the stop bar (LocalY = 350) and up to 100 feet upstream of the stop bar (LocalY = 250).  The vehicle speeds (shown in feet per second) are shown in the circles, again at ten foot increments.  One question that this raises: when we talk about saturation flow rate and saturation headways, we have traditionally meant with respect to the stop line.  But when we take a broader view of saturation headway or flow rate, we see that for the queue clearance period, the headways are longer as the queue begins to move, and then shorten as the queue picks up speed.  For example, consider the headways between the third and fourth vehicles (90 and 144): as the queue begins, the headway is 5.2 seconds at fifty feet upstream of the stop line.  The headway decreases to 3.3 seconds, when the vehicles pass by the stop line (at LocalY = 350).  This finding may have an implication for traffic signal settings (passage time and minimum green time) when the detection zone is located upstream of the stop bar.

Lane 1, Group 2
In the second cycle (group 2), two vehicles (235 and 239) have arrived during red.  The following two vehicles (254 and 266) arrive during green but are delayed by the departing queue.  Even the next two vehicles (270 and 272) are traveling slower than their desired speed and are affected by the departing queue.  They are traveling between 10 and 33 feet per second between between the stop bar and 100 feet upstream of the stop bar.  The final two vehicles (296 and 319) are traveling at normal speeds (between 34 and 53 feet per second) and don't seem to be affected by the departing queue.

As we saw in group 1, the departure headways decrease as the measurement location moves from upstream to the stop bar. For example, the headway between vehicles 235 and 239 is 3.8 seconds at LocalY = 340 feet but decreases to 2.5 seconds just past the stop bar (LocalY = 350 feet).  A similar trend is evident between the second and third vehicles (239 and 254).  The headway is 2.8 seconds at LocalY= 320, but decreases to 1.7 and 1.6 seconds as the measurement location reaches the stop bar.  For vehicles that are less affected by the departing queue, there is less variation in the headways.  The headways for vehicles 4 and 5 (266 and 270), the headway is 3.9 seconds at LocalY = 300 feet and 3.8 seconds at LocalY = 350 feet.

Lane 1, Group 3
In this group, there are four vehicles in the queue at the beginning of green.  The final two vehicles (480 and 482) arrive after the beginning of green and seem unaffected by the departing queue.  We see a similar trend as above for vehicles 2 and 3 (392 and 411).  The headway between these vehicles is 3.8 seconds at LocalY = 300 but is has decreased to 1.6 seconds at LocalY= 350 feet.

Lane 1, Group 4

Lane 1, Group 5
This group contains two vehicles that are not part of the same cycle.  No data analysis was conducted.

Lane 1, Group 6
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