1. Visibility of ‘Weathered’ Fluorescent Colored Highway Signs Brandon Jerred, Matthew Dewald, Mackenzie Mertz and Aubrey Milton Department of Psychology, University of South Dakota (Faculty Sponsor: Frank Schieber)
ABSTRACT
The color saturation (vividness) of fluorescent colored highway signs fades in a deterministic fashion given long-term exposure to the sun (i.e., weathering). We conducted a laboratory study to assess the effects of such weathering upon sign visibility. Scale models of diamond-shaped highway signs were constructed from actual samples of fluorescent orange highway sign sheeting material that had been subjected to varying degrees of accelerated weather exposure. The time needed to search for and find each sign when embedded against a photo-realistic background in our lab’s solar simulator was recorded in a sample of 30 observers. Significant increases in visual search time were found to accompany increasing sign weather exposure. We report the relationship of this decline in visual conspicuity relative to the characteristic changes in luminance and color saturation that accompany normative sign weathering. The results will be used by the Federal Highway Administration to guide the development of photometric performance standards.
METHOD
Subjects. Thirty (30) students recruited from classes at USD served as observers. Participants ranged from years of age and had normal acuity and color vision.
Apparatus and Materials. Ten (10) categories of fluorescent orange highway sign sheeting were examined. New samples of non-fluorescent orange (sign-1) and fluorescent orange (sign-2) material were used to establish standard and optimal visual performance baselines, respectively. Eight (8) samples of “weathered” fluorescent orange sheeting material were supplied from the FHWA sign inventory. These signs varied in their degree of weathering, ranging from mild (sign-3) to severe (sign-10). The sign stimuli were illuminated using a sunlight simulator and were presented at a distance of approximately 25 ft. Stimuli were viewed through a large electrochromic “glass shutter” so that their presentation onset time could be precisely controlled by computer. Sign stimuli were 2-inch squares that were presented at various positions against a high resolution, color-realistic background composed of a computer-enhanced photograph depicting a residential street (see mockup).
Procedure. On any given trial, an experimental stimulus signs was mounted at one of 6 predetermined locations on either the left of right side of the photo-realistic background scene in the sunlight simulator. Next, the electrochromic window was opened and the participant was required to search the scene for the target sign and signal its location (left vs. right side) as quickly as possible via a push button console. A computer was used to determine the participant’s search time with millisecond precision and accuracy. Each of the 10 orange signs was presented twice at each of the 6 possible background positions for a total of 120 stimulus trials. Stimulus order and location was randomized across trials.
Photometric Analysis of Weathered Sign Stimuli
Sign cd/m2 Chroma Saturation Chromaticity
, 0.365
, 0.358
, 0.347
, 0.351
, 0.370
, 0.372
, 0.356
, 0.368
, 0.386
, 0.391
RESULTS
Search Time Analysis
(8) Weathered Colors by (6) Positions ANOVA
Color F(7,175) = 7.86, p < 0.000
Post-hoc: Search times greater than Fluorescent Orange baseline:
Sign 8 F(1,25) = 12.4, p < 0.002
Sign 9 F(1,25) = 23.9, p < 0.000
Sign 10 F(1,25) = 12.4, p < 0.002
Intra-sign comparisons:
Sign 9 vs F(1,25) = 8.75, p < 0.007
Sign 9 vs. 10 F(1,25) = 12.54, p < 0.002
THE ONLY SIGNS THAT TOOK SIGNIFICANTLY LONGER TO FIND THAN THE FLUORESENT ORANGE BASELINE (SIGNS 8, 9, 10) WERE ALSO THE ONLY ONES THAT FAILED TO OUT PERFORM THE NON-FLUORESCENT ORANGE BASELINE.
CONCLUSION: WHEN FLUORESCENT COLORED SIGNS NO LONGER YIELD VISIBILITY SUPERIOR TO NON-FLUORESCENT COUNTERPARTS THEY SHOULD BE REPLACED.
FUTURE RESEARCH:
---GENERALIZE RESULTS TO A VARIETY OF BACKGROUNDS
---EXPLORE FLUORESCENT YELLOW AND YELLOW-GREEN
INTRODUCTION
The Manual of Uniform Traffic Control Devices (MUTCD) codifies the Federal Highway Administration’s regulations regarding the design and deployment of signs on the nation’s streets and highways. The Millenium Edition (2000) of the MUTCD permitted the use of three new highway sign colors: fluorescent orange, fluorescent yellow and fluorescent yellow-green. These fluorescent colors are reserved for special applications were high conspicuity safety warnings are necessary (for example: work zones, hazardous intersections and school crossings).
Fluorescent colored signs are clearly more conspicuous than their non-fluorescent counterparts (Burns, et al., 1999; Schieber, 2002). The visibility advantage of fluorescent colored signs appears to be due to their enhanced daytime luminance and high color purity (saturation). However, these enhanced properties are compromised after prolonged exposure to the sun and severe weather conditions.
Recently, the Federal Highway Administration (FHWA) announced a rule-making initiative in which minimum performance standards for fluorescent colored highway sign materials would be developed for inclusion in the MUTCD. One approach to developing such standards is to collect a range of fluorescent colored sign materials that have been allowed to “weather” for various periods of exposure; and, assess how changes in the photometric properties (brightness, chromaticity, saturation) of these progressively weathered materials influence visual performance. The work reported here represents one of several initial efforts designed to investigate the relationship between the “aging” of fluorescent colored sign materials and their subsequent visibility. This research represents a cooperative effort between the FHWA Photometrics Laboratory and the Heimstra Human Factors Laboratories of the University of South Dakota.
WEATHERING-RELATED DECREASES IN SATURATION (COLOR PURITY) ACCOUNT FOR 59% OF THE VARIATIONS IN VISUAL PERFORMANCE; LUMINANCE CHANGES ACCOUNT FOR ONLY 19%
COLOR PURITY (SATURATION) DECLINES SYSTEMATICALLY WITH INCREASED WEATHER EXPOSURE.