Sag Vertical Curve Design Criteria for Headlight Sight Distance (2013) / Chapter Skim
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Pages 88-92
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86 CHAPTER 7 DISCUSSION ON AASHTO GUIDELINES The potential changes to the AASHTO policy on the design of sag vertical curves discussed in Chapter 5 – a result of the literature review and survey – must be reconsidered with the additional data from the visibility experiments. A review of each solution follows.
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87 Figure 43. Mean detection distance for pedestrians by clothing and age (Source: Wood, Tyrrell, & Carberry, 2002)
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88 Using AASHTO's values for brake reaction time, and a visibility distance of 230 ft, we find the deceleration rates required to stop in that distance by design speed. Table 38 shows these results.
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89 Discussion of the Appropriateness of SSD The AASHTO design requirements for sag vertical curves are based on four factors: headlight SD, passenger comfort, drainage control, and general appearance. The headlight SD is typically the primary factor, however, because: 1)
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90 Figure 44. K values for sag vertical curves.
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