Sag Vertical Curve Design Criteria for Headlight Sight Distance (2013) / Chapter Skim
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51 CHAPTER 5 POTENTIAL CHANGES TO THE AASHTO POLICY Based on the results of the literature review and the practitioner survey, modifications to the AASHTO methodologies can be considered. As there were very few exceptions to the AASHTO methodologies, the confines of the existing methods must be considered.
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52 To ensure a long enough SD, the headlight SDs at an angle of 1º, which are equal to the stopping SDs, were used in equation (2) to re-calculate the curve lengths needed under different uplight angles.
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53 SOLUTION A.1: INCREASE DECELERATION RATE According to AASHTO, the current SSD assumes that: 1) the reaction time is 2.5 s, and 2)
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54 Although increasing deceleration rate can be obtained in some cases, given a satisfactory road surface, tire quality, and weather condition, it is not always an efficient solution. A third solution is therefore proposed.
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55 ISSUES FOR THE POTENTIAL GUIDELINE RECOMMENDATIONS 1. The changes in headlight angles do affect the design of sag vertical curves due to a decreasing of SD.
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