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Federal Highway Administration Research and Technology
Coordinating, Developing, and Delivering Highway Transportation Innovations

This report is an archived publication and may contain dated technical, contact, and link information
Publication Number: FHWA-HRT-04-140
Date: December 2005

Enhanced Night Visibility Series, Volume IX: Phase II—Characterization of Experimental Objects

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To travel safely during darkness, the human visual system must adapt from daylight sensitivity to darkness sensitivity. For the task of driving in the dark, the detectability of objects on the roadway becomes critical, and a vehicular vision enhancement system (VES) is required. Traditionally, a VES has been considered to be vehicle headlamps only, but with the development of new technologies, a VES can be headlamps in conjunction with ultraviolet (UV–A) sources, infrared (IR) technology, or camera-dependent systems. Their effectiveness and effect on the driver vary based on the type of technology used.

The Enhanced Night Visibility (ENV) project is a series of experiments undertaken to investigate different VESs for the nighttime driving task. The execution of this project was conducted in three phases, one as a preliminary study and the other two at the contractor’s facility. This report is particularly concerned with the experiments conducted in Phase II, the first performed at the contractor’s facility. In this set of visual performance experiments, detection and recognition distances of 12 different VESs were measured. Detection distance was defined as the distance in front of the vehicle at which an object can just be seen. Recognition distance was defined as the distance at which the object can be clearly identified. For these experiments, the objects represented real hazards on the roadway such as pedestrians, cyclists, tire treads, and bicycles. In total, nine objects differing in size and shape were used for the experiments.

The purpose of this portion of the ENV project was to establish the photometric nature of the objects presented to the observer. The photometric measurements of interest were the headlamp illuminance, object luminance, and the object background luminance. Other calculated parameters were established such as object contrast with the background, reflectance of the objects, luminance of the object background, and object visibility.

Even though the Phase II visual performance experiments used up to nine objects and 12 VESs, this activity characterized only eight object types and 11 VESs. Two of the Phase II objects were similar in appearance, so they were characterized as one object. The visible light produced by the Phase II IR VES came from a headlamp system shared by another VES, so the IR VES was excluded from characterization.

This investigation sought to answer the following research questions:

  1. What is the correlation between the photometric performance of the VES and visual detection and recognition performance from the Phase II ENV visibility studies (ENV Volumes III, IV, V, and VI)?
  2. Of the visibility metrics analyzed, what threshold values are required for detection and recognition of the objects tested?
  3. What is the effect of different weather conditions on the visibility of the tested objects?

This report presents an indepth analysis of the visibility of the objects in clear weather to answer the first and second questions. The effect of the weather is then considered based on the results from the clear investigation.


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