Recent Roadway Geometric Design Research for Improved Safety and Operations (2012) / Chapter Skim
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Pages 6-11
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be added to the Green Book. The researchers did not identify a need to update the Green Book design criteria for sight distance, lane width, horizontal curves, cross-slope breaks, or vertical clearance to better accommodate trucks.
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] design vehicle (Harwood et al.
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2003a) In addition to including the survey of practice and information on the relationships between speed and various geometric and traffic factors, the report lists suggested refinements to the Green Book in the following areas: design speed definitions, information on posted speed and its relationship with operating speed and design speed, how design speed values were selected in the United States (noting that anticipated posted speed and anticipated operating speed were also used in addition to the process in the then-current edition of the Green Book, which is based on terrain, functional class, and rural versus urban)
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is not exceeded by the required SSD. The inferred design speed may also be limited by a combination of lane width and average daily traffic (ADT)
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geometric design features." A value equal to or slightly greater than the target speed (i.e., the desirable free-flow operating speed) is appropriate for work zone design speed.
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. • Observation of driving behavior revealed that the strongest indicator of operating speed was posted speed limit.
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