ASSESSMENT OF NIGHTTIME ROADWAY VISIBILITY

APPROXIMATELY SEVEN VISIBILITY METERS HAVE BEEN DESCRIBED IN THE LITERATURE DURING THE LAST 20 YEARS. THE SALIENT FEATURES OF EACH OF THESE INSTRUMENTS ALONG WITH THEIR LIMITATIONS AND APPLICATIONS ARE BRIEFLY DISCUSSED. THE U.C. VISIBILITY METER IS DISCUSSED IN DETAIL. THE DESIGN EQUATIONS OF THE U. C. VISIBILITY METER ARE GIVEN TOGETHER WITH THE CRITERIA FOR A SUITABLE VISIBILITY METER. DETAILS OF OPTICAL PARTS AND CALIBRATION ARE INCLUDED TO SHOW COMPLIANCE WITH THE DESIGN CRITERIA. THE U. C. INSTRUMENT HAS BEEN USED TO EVALUATE THE VISIBILITY CONDITIONS OF TWO EXTREMES OF STREET LIGHTING, THAT IS, A UNIFORM AND AN EXTREMELY NON-UNIFORM ROADWAY BRIGHTNESS PATTERN. UNDER EACH CONDITION A TWO-DIMENSIONAL AND A THREE DIMENSIONAL TARGET WAS USED TO GATHER INFORMATION. RESULTS OF THESE ROADWAY STUDIES ARE PRESENTED. THESE RESULTS SHOW A GREAT VARIATION IN VISIBILITY UNDER THE NON-UNIFORM ROADWAY BRIGHTNESS PATTERN AND LESS VARIATION IN VISIBILITY UNDER THE UNIFORM ROADWAY BRIGHTNESS PATTERN. THE PEAK VISIBILITY OF THE NON- UNIFORM CONDITION IS ONLY SLIGHTLY GREATER THAN THE AVERAGE VISIBILITY LEVEL OF THE UNIFORM CONDITION. /AUTHOR/