Highway Capacity Manual Methodologies for Corridors Involving Freeways and Surface Streets (2020) / Chapter Skim
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Pages 10-13
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From page 10... ...
- 4 - 2. Literature Review A review of the literature regarding operational effects of freeway-urban street interactions yielded a limited number of publications.
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From page 11... ...
- 5 - spillback, but the HCM Freeway Facilities procedure does not account for this delay caused by queue spillback into the mainline. Rather, average travel speed is estimated and the difference between that and the freeway's free-flow speed can be used to estimate delay.
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From page 12... ...
- 6 - Based on the review of the literature, we can conclude that estimating operational measures in the case of spillback from an off-ramp analytically is challenging, as it is very difficult to anticipate the wide variety of driver actions. The following trends and observations documented in previous research are used in this research to develop the framework of the proposed methodologies: • Discharge flows along the mainline are affected by the presence of an off-ramp queue, with one study observing 4,520 vehicles per hour on a three-lane freeway mainline (≈ 1,500 veh/h/ln.)
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From page 13... ...
- 7 - In conclusion, there are tools available to estimate the lost time incurred at the upstream intersections as a function of a downstream queue length and storage availability. Still, extensive field observations are necessary to document discharge rates at congested on-ramps and based on these estimate the resultant queue length along the on-ramp.
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