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