Capacity Analysis of Interchange Ramp Terminals Final Report (1997) / Chapter Skim
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APPENDIX B Field Study Data Collection and Reduction
APPENDIX B Field Study Data Collection and Reduction
Pages 177-204
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From page 177... ...
quantifies the effect of downstream traffic conditions on the traffic characteristics used to estimate the capacity of lefr-tum and through movements at interchange ramp terminals arid adjacent intersections. These characteristics include start-up lost time, saturation flow rate, arid clearance lost time.
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From page 178... ...
This model can be used to convert a predicted queue length from the number of equivalent passenger cars to units of distance (e.g., meters)
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Capacity Utilization Length Traffic Discharge Headway Cat haractenstics | Discharge Speed | C l l l Start-Up Lost Time C Count & Location of Cars on Be Downstream Link at He 5~ of Offs'' Queued Driver ' Wing Reaction Time ~| | V | Queued Vehicle Storage Length l l | V l Traffic Demands by Lane and Movement | TravelPa~Mat ix(O-D's) | | V I ; Weave & Non-Weave Vehicle Travel Tune | Weave & Non-1 'cave Flow Rate per Lane l l l Performance Saturation Flow Rate C .
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A typical data collection setup for this study is shown in Figure B-2. Queue length arid starting reaction time data, needed for the Queue Length Model, were collected with both study types.
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. it:: Boundary of / Study Zone LEGEN D "< ond field of view ,~ Tape Switch Sensor 7 Photocell Sensor ~ Tape Switch Speed Trap Figure B-1.
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an/ ~ - ~ video Camaro \2 ~ LEGEND Comer Bounds of/ Study Zone f ~e -. If afar ~ co~ deft.
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These figures also show the locations of the tape switch sensors, photocell sensors, and video cameras. The sensors were monitored by a computer, which also served as the data processing and recording device.
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In general, the study sites satisfied almost all ofthe geometric and traffic demand criteria previously described. In a few instances, the distance to the adjacent Intersection exceeded the desired 275-meter maximum distance; however, the traffic demands at these sites were sufficiently high as to precipitate the extensive queuing considered desirable for study purposes.
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From page 185... ...
At SPUI's, ~e "same direction" concept is also applied but the opposing direction through stop line is used as the reference point at the second ramp terminal (since the Trough stop line at the second ramp terminal does not exist at the SPUI)
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From page 186... ...
B.3 DATA COLLECTION B.3.1 Approach Cycle Length2 (see) 26, 105 82, 90 90 90 100 90,120, 128 3 90 0 24 90 78,90, 102 The data collection equ~pment used to collect the field data included v~deo cameras and computer-monitored tape switch sensors placed in the traf Eic lanes.
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From page 187... ...
Data collected dunng the capacity studies were used to calibrate the capacity and lane utilization models. Data for the capacity mode} were collected using bow the computer-mon~tored tape switches arid the video recorders at each of the twelve Interchange study sites.
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nit a' Camera 1 Figure B-3. Typical data collection equipment locations for a capacity study.
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Figure B-4. Fields of view for the capacity study camera locations shown in Figure B-3.
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database. This effort was followed by the reduction of data for We queue length, capacity, arid lane utilization models.
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Typical data collection equipment locations for a weaving study.
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Figure B-6. Fields of view for the weaving study camera locations shown in Figure B-S.
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From page 193... ...
When the wave arrives, it results In longer discharge headways as the affected vehicles begin to "crawl" over the stop line in a highly-congested state. Finally, after Me wave passes, the density steadily decreases (due to the downstream green, see Field/column S)
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From page 194... ...
in queue & arrivals after queue) L Vehicle Count - number of queued vehicles served since start of phase M Discharge Time - time back axle of vehicle crosses stop line/tape switch relative to start of phase N Discharge Headway -headway between subject vehicle back axle and preceding ~rehicle back axle O Wheelbase - subject vehicle wheelbase P Discharge Speed - subject vehicle speed when crossing the stop line/tape switch Q Acceleration/Deceleration - subject vehicle acceleration when crossing the stop line/tape switch R Zone Counts - number of vehicles in each 30-meter zone in downstream lane (left to right - up to downstream)
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The assembled queue length database contains queue length and reaction time measurements for 122 Brst-in-queue passenger cars and 1,053 last-~n-queue passenger cars. This data was obtained at eight of Me twelve study sites.
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During video playback, vehicles entering the study section were tracked as they proceeded Tom the upstream ramp terminal to the adjacent, downstream intersection. This tracking required recording the manner in which the vehicles entered (i.e., off-ramp right-turn or arterial through movement)
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From page 197... ...
The transition periods between signal timing Claris at these sites tended to produce a few, extremely long cycle lengths that led to the high variability in cycle length that was observed at the study sites. The average minimum discharge headway and corresponding saturation flow rate are summarized ~ Table B-7 for He two junction and movement types studied.
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From page 198... ...
3 - Computed as 3,600 divided by the minimum discharge headway. 4 - Based on tibe average headway of He fit through last queued passenger car able to discharge prior to queue Spillback Dom He downstream intersection.
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The data in Table B-9 indicate Mat the average clearance lost time is about 2.77 seconds. This value is within the range of I.2 to 2.8 seconds recognized by the 1994 Highway Capacity Manual (1, Chapter 2)
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The lane coinciding with Me maximum demand flow rate was often found to vary each cycle. The lane utilization factors computed for the through movement lane groups at the twelve study sites are shown in Table B-IO.
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Database Summaty The analysis of the queue length mode] database focussed on We computation of the average lane length occupied by a queued passenger car and the average queued driver starting reaction time.
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The average reaction times floured in this research are generally consistent with hose reported in We literature. Specifically, the study by Messer and Fambro 629 found that the first queued driver required about 2.0 seconds of reaction time and that subsequent queued drivers required about ~ .0 seconds.
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From page 203... ...
This speed related the distance traveled through the weaving section to the corresponding travel time. The distance and time were measured from the point of entry to the weaving section to the downstream intersection stop line or to the first point of joining the stopped queue associated with the downstream signal, whichever was reached first.
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