Evaluation of the 13 Controlling Criteria for Geometric Design (2014) / Chapter Skim
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Pages 62-67
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62 S E C T I O N 5 This section of the report addresses refinement of the definitions for the 13 controlling criteria to reduce overlaps and confusion in how they are applied in a typical design exception process. The discussion also addresses potential modifications to the list of controlling criteria.
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63 in greater likelihood of a crash. These issues need to be sorted out in future HSM editions based on valid research.
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64 for slopes steeper than 1V:4H. The horizontal clearance, being renamed lateral offset in the 2011 edition of the Green Book (5)
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65 • There is one controlling criterion for horizontal alignment that includes horizontal curve radius, superelevation, and pavement/shoulder slope breaks and a separate controlling criterion for normal cross slope Of these alternatives, the former approach appears preferable because the latter preserves the term "horizontal alignment" as a controlling criterion, even though not all elements of horizontal alignment are included in that criterion. 5.1.6 Grade, Vertical Alignment, and Stopping Sight Distance FHWA policy includes separate controlling criteria for grade, vertical alignment, and stopping sight distance.
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66 based on the likelihood of vehicles running off the road and striking roadside objects. Thus, the 4- and 6-ft lateral offset criteria are not intended as operational offsets, but rather appear to represent "mini-clear-zone" criteria.
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67 5.3 Other Potential Controlling Criteria for Design Consideration was given in the research to whether additional design elements might be considered in the future as controlling criteria for design. It is suggested that factors for adding a design element as a controlling criterion would include the following: • Known traffic operational and safety effects • Traffic operational and safety effects large enough to warrant inclusion as a controlling criterion for design • Within the scope of this research and the existing controlling criteria (which exclude design elements related to intersection design, roadside design, and access control)
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