Highway Capacity Manual Methodologies for Corridors Involving Freeways and Surface Streets (2020) / Chapter Skim
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Pages 33-40
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From page 33... ...
- 27 - 6. Queue Spillback into Urban Streets Queue spillback into an urban street occurs due to insufficient merging capacity in a freeway on-ramp, and may have the following causes: • Insufficient capacity at the freeway merge segment, per guidance provided on HCM Chapter 14 – Merge and Diverge Segments; • Insufficient capacity of the on-ramp (HCM Exhibit 14-12)
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From page 34... ...
- 28 - 1. Mainline detectors: Data were obtained from loop detectors located upstream and downstream of the merge area, providing lane-by-lane speed/volume/occupancy measurements, with resolution of 1 minute or less.
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- 29 - Table 4 – Summary of study locations – field data collection – on-ramp queue spillback Location Interchange type Intersection type Number of on-ramp lanes # video observations Atlanta/GA - I-285W NB @ South Cobb Dr NB Diamond Signalized 2 9 Atlanta/GA - I-285W SB to Cobb Pkwy Dr. Diamond Signalized 1 10 Atlanta/GA - I-285W NB to Cobb Pkwy Dr.
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- 30 - Source: Photo provided by the Georgia Department of Transportation and Google Maps Figure 26 – I-285 NB @ South Cobb Dr. and affected movements by on-ramp queue spillback: (a)
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- 31 - Source: Photos provided by the Georgia Department of Transportation and Google Maps Figure 27 – I-285W SB @ Cobb Pwky Dr. and affected movements by on-ramp queue spillback: (a)
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- 32 - San Diego, CA - Friars Rd. @ I-15 NB This partial cloverleaf interchange connects the I-15 NB freeway facility to the Friars Rd.
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- 33 - • No occurrence of incidents, disabled vehicles, lane closures or other factors that may affect the natural dynamics of vehicular traffic; During the data reduction, the following were measured: • Displayed green for each movement during each cycle; • For movements discharging into the on-ramp: the observer noted whether the subject movement experienced blockage during the given cycle. (Blockage was defined as the occurrence of queue spillback during the green, negatively impacting its discharge rate.)
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From page 40... ...
- 34 - Simulated Sites The use of microsimulation is especially important for on-ramp queue spillback, due to the difficulties collecting data for unsignalized intersections. The same interchanges used for simulation of off-ramp queue spillback were used to simulate on-ramp queue spillback.
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