Highway Capacity Manual Methodologies for Corridors Involving Freeways and Surface Streets (2020) / Chapter Skim
Currently Skimming:
Pages 20-32
The Chapter Skim interface presents what we've algorithmically identified as the most significant single chunk of text within every page in the chapter.
Select key terms on the right to highlight them within pages of the chapter.
From page 20... ...
- 14 - 5. Queue Spillback into Freeways Queue spillback into freeway facilities occurs due to insufficient capacity in at least one element of the off-ramp, namely the ramp proper or the downstream ramp terminal.
|
From page 21... ...
- 15 - Figure 4 – Data collection framework for queue spillback into freeway facilities 1. Video Cameras: video observations are the most critical data for the study of queue spillback, as they provide information that cannot be accurately captured by loop detectors.
|
From page 22... ...
- 16 - Figure 5 – Survey for off-ramp queue spillback study sites – outcome by state Dataset Description Several potential locations were selected for data collection, and only those that met all the criteria previously described were kept in the final dataset. For the selected locations, detector data were extracted from online repositories for each State DOT.
|
From page 23... ...
- 17 - Table 2 – Summary of study locations – data collection – off-ramp queue spillback LOCATION D ir ec tio na l la ne s Se gm en t T yp e D ow ns tr ea m R am p Te rm in al O ffR am p La ne s V id eo O bs er va tio ns Pe ak P er io d Sp ill ba ck R eg im e Miami/FL - I-95 SW 25th Rd. 3 Diverge Signalized Intersection 2 13 PM 4 Tampa/FL - I-275 NB to W Kennedy Blvd 4 Diverge Freeway Merge 2 6 PM 4 Norfolk/VA - I-64 WB to Northampton Blvd 4 Diverge Signalized Intersection 2 10 PM 3 Centreville/VA - I-66 WB to SR-28 (Sully Rd)
|
From page 24... ...
- 18 - Source: Photo provided by CATT Lab (Ritis.org) Figure 8 – Norfolk, VA – I-64 WB to Northampton Blvd Source: Photo provided by CATT Lab (Ritis.org)
|
From page 25... ...
- 19 - Source: Photo provided by the Georgia Department of Transportation Figure 12 – Atlanta, GA – I-285 NB to I-20 Source: Photo provided by the Florida Department of Transportation Figure 13 – Miami, FL – I-75 SB to SR 826 Source: Photo provided by the Georgia Department of Transportation Figure 14 – Atlanta, GA – I-285 NB to GA-141 Source: Photo provided by the California Department of Transportation Figure 15 – Sacramento, CA – SR-99 NB to SR-50
|
From page 26... ...
- 20 - Data Reduction Video observations were the most challenging part of the data reduction, as the process of obtaining the recordings was very time-consuming. After the recordings were obtained from the respective agencies, the research team performed a first screening at the videos for an initial validation, which included the following conditions: • Camera is able to show the queues in the diverge area as required for project purposes; • No occurrence of incidents, disabled vehicles, lane closures or other factors that may affect the daily dynamics of vehicular traffic; • No overlapping bottlenecks – the off-ramp is the only source of congestion.
|
From page 27... ...
- 21 - Figure 17 – Sample of data illustrating queue spillback: (a) queue length and (b)
|
From page 28... ...
- 22 - Source: Photos provided by (a) CATT Lab (Ritis.org)
|
From page 29... ...
- 23 - When the segment is a lane-drop (rather than a diverge) the exiting traffic can access the off-ramp with a single lane change.
|
From page 30... ...
- 24 - available according to the position of detectors and were different for each study location. For the simulated sites, detector stations were placed at three locations upstream of the exit: 1,500 ft, 4,000 ft and 8,000 ft.
|
From page 31... ...
- 25 - Queue Spillback Check The first step to evaluate queue spillback into freeways is to assess whether it is expected to occur. The detailed methodology for off-ramp spillback check is provided in Appendix B - Off-ramp Queue Spillback Check.
|
From page 32... ...
- 26 - Evaluation of Queue Spillback Impacts If queue spillback is expected to occur, the analyst must refer to the procedure for evaluation of impacts of queue spillback, described under Appendix C - Off-Ramp Queue Spillback Analysis. The procedure takes an approach similar to the Oversaturated Segment Evaluation (HCM Chapter 25)
|
Key Terms
This material may be derived from roughly machine-read images, and so is provided only to facilitate research.
More
information on Chapter Skim is available.