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原文传递 Sag Vertical Curve Design Criteria for Headlight Sight Distance.

题名：	Sag Vertical Curve Design Criteria for Headlight Sight Distance.
作者：	Du, J.; Gibbons, R. B.; Medina, A.; Rakha, H.; Williams, B.
关键词：	Design Criteria; Headlamps; Methodology; Reviews; Sag Vertical Curve; Sight Distances; Surveys; Technology Assessment; Visibility
摘要：	This document is the final report for NCHRP Project 15-41, Sag Vertical Curve Design Criteria for Headlight Sight Distance. This report includes a review of the current methodologies used in the design of sag vertical curves, a review of the changes in headlamp technologies, the results of the survey of practitioners, two visibility experiments, and discussion on potential changes to the American Association of State Highway and Transportation Officials (AASHTO) design guide. The review of the headlamp technology shows that, over time, headlamp technologies have had increasing limitation on the amount of light emitted above the horizontal axis of the headlamp. In addition to the regulatory impact, headlamp technologies such as visually optically aligned technologies also limit uplight. In the practitioner survey, it was found that very few deviations from the AASHTO design methodologies were used. Based on the practitioner review, the potential to modify the current methodologies is limited to the manipulation of the vehicle speed, deceleration, and the angle of curvature change. The results of the visibility experiments found that participants detected objects at distances which were significantly shorter than the safe stopping distance (SSD). This occurred not only in sag vertical curves, but also on flat roadway. This indicated that even if sag vertical curves were redesigned, visibility distance would still be shorter than SSD because the headlamps would be the limiting factor. A review of the potential modifications to sag vertical curve designs (which were suggested as a result of the practitioner survey) found that these changes would be inadequate to make up the difference between visibility distance and SSD.
报告类型：	科技报告