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Federal Highway Administration Research and Technology
Coordinating, Developing, and Delivering Highway Transportation Innovations
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Publication Number: FHWA-HRT-04-132
Date: December 2005
Enhanced Night Visibility, Volume I: Executive Summary
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Timely detection of traffic control devices and hazards on the roadway is an essential part of safe driving at night. There is general agreement that automobile low-beam headlamps provide, at best, marginal visibility for low-contrast objects such as pedestrians.(1) Therefore, alternative systems that enhance night visibility are needed, especially systems that enhance pedestrian detection. Preliminary studies have indicated that prototype UV–A headlamps significantly improve visibility for fluorescent traffic control devices and for pedestrians.(2,3,4)
The purpose of the Enhanced Night Visibility (ENV) project was to study supplemental ultraviolet A (UV–A) headlamps, supplemental infrared (IR) systems, various headlamp technologies, and supporting infrastructure to improve drivers' ability to detect and recognize objects and pedestrians at night. The project will be of interest to headlamp designers, automobile manufacturers and consumers, third-party headlamp manufacturers, human factors engineers, and those involved in headlamp and roadway specifications.
The project initially focused on the potential for implementing UV–A and its supporting infrastructure. Phase I established the plan to facilitate implementation of UV–A headlamps. Phase II was a series of six studies with the primary objective of facilitating the implementation of UV–A technology. Four of the studies were object detection and recognition studies (i.e., visual performance studies) that separately examined visibility in clear weather (ENV Volume III), rain (ENV Volume IV), snow (ENV Volume V), and fog (ENV Volume VI). Another study was conducted to assess oncoming drivers' level of discomfort glare caused by UV–A headlamps relative to other vision enhancement systems (VESs) (ENV Volume VII). The sixth study conducted in Phase II evaluated the visibility of 3 different pavement markings in combination with 11 VESs (ENV Volume VIII). VESs in Phase II of the ENV project included headlamps alone or headlamps in combination with a supplemental system such as UV–A or infrared thermal imaging system (IR–TIS).
Originally Phase III was planned to be a public-road study to further assess the benefit of supplemental UV–A; however, the results of the Phase II testing indicated that supplemental UV–A did not produce sufficient improvement to justify further testing. On the other hand, IR–TIS did show sufficient benefit to be tested further. Phase III of this project shifted the emphasis from supplemental UV–A to supplemental IR. Three studies were conducted in this phase. Two visual performance studies, one in clear weather (ENV Volume XIII) and one in rain (ENV Volume XIV), tested both IR–TIS and near IR systems as well as headlamps alone. The third study (ENV Volume XV) assessed the discomfort glare and disability glare of five different headlamp systems.
In total, the ENV project included 6 studies of visual performance, in terms of object detection and recognition, while using 18 different VESs ranging from halogen (i.e., tungsten-halogen) to UV–A and IR technology. All of the VESs were tested in clear weather conditions, and subsets of the VESs were tested in adverse weather conditions, including rain, fog, and snow. Subsequent analyses characterized the luminance of the objects for each VES used in the visual performance studies (i.e., detection and recognition testing) (ENV Volumes IX and XVI) and characterized the VESs (ENV Volume XVII). Two studies evaluated discomfort glare to oncoming drivers from 14 of the VESs and disability glare to oncoming drivers from 5 of the VESs. An additional study assessed pavement marking detection using 11 of the VESs.