Traffic Queue Length. A major concern about a TSP system is whether a TSP treatment will cause excessive delay for other intersection movements. To address this concern, a key MOE is the size of the traffic queue for each conflicting phase and the delays associated with those queues. Before and after analysis of traffic queue lengths can help answer whether queues significantly lengthen for movements not receiving the benefits of TSP treatments. Also, it helps understand TSP impacts on streets crossing the TSP corridors. In this study we manually collected sample traffic queue length data from recorded video images at TSP-enabled intersections within the SS-RTSP project. Signal Cycle Failures Signal cycle failures refer to the specific delay condition in which vehicles must sit through at least one complete signal cycle to pass through an intersection. This condition leads to considerable public frustration, and an increased occurrence of such failures is likely to result in more substantial “public resistance” to TSP than will a minor increase in intersection delay. Thus, it is a key measure reported to public officials. Signal cycle failures were extracted manually from recorded video data.
Traffic Queue Length. We manually counted the traffic queue length in vehicles from field recorded video data. Table 8-8 shows the traffic queue lengths on cross-streets. Because of time constraints, we analyzed and summarized data only from Mondays. Table 8-8 Traffic Queue Length on Cross Streets in Phase One Test Intersection Cross-Street Average Queue Length Per Cycle Standard Deviation Maximum Median TSP Off Alderwood Mall Parkway South approach 2.65471 2.41476 14 2 Alderwood Mall Parkway North approach 1.56651 1.31575 7 1 36th Ave West approach 3.20079 2.58121 16 3 TSP On Alderwood Mall Parkway South approach 2.64318 2.43128 12 2 Alderwood Mall Parkway North approach 1.63679 1.40252 7 1 36th Ave West approach 3.27135 2.76868 16 3 We also used a paired t-test to compare the average queue length before and after TSP implementation. The t ratio was -1.578, the absolute value of which was smaller than the critical t ratio of 2.920 at p=0.05. Therefore, the change of the average queue length on cross-streets after the SS-RTSP implementation was not significant. The average traffic queue length slightly increased for about 0.07 vehicles per signal cycle when the TSP system was turned on. However, on the southbound corridor of the Alderwood Mall Parkway intersection, traffic queue length decreased for about 0.01 vehicles per cycle. This result may be due to regular traffic variations between the two study days. Standard deviations of queue length also increased a little for all three cross- streets when TSP was on. The maximum queue length stayed at almost the same level after the TSP implementation. On the southbound corridor of the Alderwood Mall Parkway intersection, the maximum queue length even decreased for two vehicles per cycle when the TSP system was on. The median value of traffic queue length remained constant before and after the implementation of the TSP system.
Traffic Queue Length. We manually counted the traffic queue lengths from field recorded video tapes. Because of time constraints, this analysis was conducted on two representative intersections on the SR 99 corridor. Table 9-8 shows the statistics for traffic queue lengths on the cross-streets of the two intersections. 164th Street Eastbound 4.412 2.377 12 4 174th Street Westbound – through 1.353 1.433 5 1 174th Street Westbound – Left turn 0.647 0.597 2 1 174th Street Eastbound– through 0.800 1.476 8 0 174th Street Eastbound– Left turn 3.983 2.344 12 4 TSP On 164th Street Westbound 4.471 3.229 13 3 164th Street Eastbound 3.829 2.172 10 4 174th Street Westbound– through 1.909 1.258 6 2 174th Street Westbound– Left turn 0.338 0.553 2 0 174th Street Eastbound– through 1.722 1.944 9 1 174th Street Eastbound– Left turn 3.654 2.591 10 4 As we can see in Table 9-8, when TSP was turned on, queue length decreased in some cases and increased in other cases. This is reflected by the unpredictable changes in queue length statistics, including standard variation, maximum queue length, and median queue length, in Table 9-8. Again, a paired t-test was applied to compare the average queue lengths at the test intersections before and after TSP implementation. The t ratio was -1.663, the absolute value of which was smaller than the critical t ratio of 1.962 at p=0.05. Therefore, the change in average queue lengths on cross-streets after the SS- RTSP implementation was not significant.
