Despite the higher accident rates during night driving compared to those in daylight, little research has been conducted onudnighttime highway safety. Nighttime sight distance is one of the most relevant factors in night driving. Current design guides provideudtwo dimensional models to study nighttime sight distance in order to design sag vertical curves. These models may, nonetheless,udunderestimate or overestimate the available sight distance because they do not take account of possible combinations with hor izontaludalignment nor the actual roadside obstructions. It is therefore necessary to develop a three-dimensional (3D) procedure capable ofudanalyzing the available sight distance under nighttime conditions. This way, it is possible to set the basis of nighttime driving safetyudresearch. Thus the study of nighttime sight distance could help in determining whether highway geometric design or headlampudfeatures may influence accident-prone locations. The aim of this study is to analyze the influence of the headlamp lightingudparameters on real highways and compare the nighttime sight distance outcome to that in daylight. A GIS-based application for sightdistanceudstudies with a specific tool for nighttime sight distance has been used. The headlamp parameters studied were beam range,udheadlamp height, upward divergence angle and horizontal spread angle. The analysis has been carried out on different real highways,udwhich enabled the study of the influence of each parameter on different 3D alignments.
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