Capacity Analysis of Traffic-Actuated Intersections Final Report (1996) / Chapter Skim
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APPENDIX H
APPENDIX H
Pages 189-206
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From page 189... ...
Properly designed short unit extensions are also expected to perform better than longer unit extensions due to snappy operation, and different unit extension and maximum green settings should result in different estimates of delay [21. The cycle length and green times presented in Appendix II of Chapter 9 of the HCM are based on the assumption that a vehicle-actuated controller wait maintain 95 percent saturation levels on the critical approach for the respective phases, an assumption that is not always correct.
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From page 190... ...
Both delay models have companion models for estimating average green time, cycle length, and degree of saturation as a function of the controller settings, phasing patterns, traffic volumes, and geometric conditions tad; however, as previously mentioned, those models are not the focus ofthis paper. Their development and validation are documented in other reports.
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From page 191... ...
This mode! (similar to the HCM delay model, but using k values between 0.04 and 0.20, depending on the unit extension values rather than a constant k value of 0.5)
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From page 192... ...
/(sg) ; arrival flow rate, veh/sec; saturation flow rate, veh/sec; green ratio, u = g/C; flow ratio, y = q/s; non-overflow term parameter; non-overflow term parameter at Id; capacity of the lane group, in vph; peak flow time period in hours, in which the mode} parameters are fixed overflow term parameter; gap setting as a headway value, see; and maximum green setting as a controller displayed value, sec.
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From page 193... ...
inputs from the field data were plugged into the proposed delay models to provide estimated delays for the conditions observed in the field. These estimated delays were then compared to measured delays from the field.
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From page 194... ...
These conditions include geographic vanation, geometric vanation, traffic variation, and signal control parameter variation, especially actuated control parameter variation (minimum green, maximum green, vehicle extensions, phase sequence, etc.) ; however, when searching for suitable study sites, selection is limited to those conditions that can be found in the field.
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From page 195... ...
University Drive at Spring Loop Data Collection As mentioned several types of data were collected at the two pilot study sites. Video and electronic data were collected for three days at each site and used to evaluate the signal timing estimation models.
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From page 196... ...
each day. Tube counters were placed at appropriate distances on each approach to record the approach volumes for the entire data collection period.
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From page 197... ...
Measured stopped delay values were manually calculated using traffic volume counts from the video tapes and queue counts perfonned In the field. The resultant measured delays were then compared to the estimated delays from the Fambro-Rouphai!
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From page 198... ...
and Table H-3 arid Figure H-4 for the Ak~elik-Chung model. Note that both proposed delay models produce similar results; i.e., estimated delays are close to measured delays for the north/ south approaches, and estimated delays are higher than measured delays for the east/west approaches.
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From page 199... ...
at FM 158 and Copperfield Drive (Ak~elik-Chung) Time ~ NortI bound ~Southbound ~Eastbound ~Westbound Period | Mc~umd Evened Measured Evened Mo~u~t End Metered EARLY& 7:15-7:30 2.3 3.2 0.7 3.1 3.0 22.3 13.1 23.8 7:30-7:45 2.1 4.2 2.4 1.7 14.3 18.6 14.0 20.5 7:45-8:00 8:00-8: 15 3.2 4.2 3.2 2.1 8:30-8:45 3.2 8:45-9:00 0.9 9:00-9:15 2.7 9:15-9:30 2.4 3.4 2.9 2.6 1.9 2.7 1.3 5.1 1.4 14.3 10.0 5.6 18.6 14.0 23.4 18.9 28.6 10.6 25.2 32.4 __ .
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From page 200... ...
Stopped Delay at FM 1SS and Copperfield Drive As noted, estimated delays on the east/west approaches to the intersection were higher than the measured delays. This discrepancy is a result of the high right-turn volume (50 percent of total traffics, the 16-foot wide approach lanes, and the fact that delays estimated on both approaches included right-turn-on-red and right-turn free-queue vehicles in the traffic volume counts.
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From page 201... ...
Stopped Delay at University Drive and Spring Loop Appendix H: Page 13
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From page 202... ...
Northbound ~Southbound ~Eastbound ~Westbound Time e °4 ~ MGS=~ Ed need M=~umd Evened M=ed ED Mood ED 3:15-3:30 31.2 31.6 40.5 31.4 3.6 15.6 4.4 16.1 3:30-3:45 40.7 28.5 33.1 33.1 5.1 16.8 4.5 17.1 3:45-4:00 58.6 49.9 50.6 48.4 3.3 13.4 6.9 13.2 4:30-4:45 69.4 48.0 52.8 45.4 4.2 16.0 7.6 15.5 4:45-5:00 57.1 45.0 60.6 46.6 4.0 17.3 6.1 17.4 5:00-5:15 50.2 47.9 53.6 47.9 9.4 21.8 22.5 19.7 5:15-5:30 70.0 45.6 s3.7 4s.7 8.8 21.6 14.4 20.8 80 ONorth XSouth AEast fewest 0 20 40 60 80 M e a s u re d S to p p e d D e la y Is e c/v e h ~ Figure H-6. Stopped Delay at University Drive and Spring Loop Appendix H: Page 14
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From page 203... ...
eastbound estimated delays decreased significantly and more closely matched the measured delays (Table H-6 and Figure H-7 for the Fambro-Rouphai! Model and Table H-7 and Figure H-8 for the Ak~elik-Chung Model)
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From page 204... ...
at University Dr. and Spring Loop (Eastbound Estimated Delay Adjusted for Progression)
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From page 205... ...
If this adjustment was made, the e~echve capacity would have been reduced, and estimated delays would have increased and more closely matched the measured delays in the field. Appendix H: Page 17
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From page 206... ...
Since current delay models do not address these conditions and neither of them is an objective of this study, selection of fixture study sites should strive to minimize their occurrence. Progression effects have a significant impact on delay in the field.
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