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Publication Number: FHWA-HRT-13-018
Date: April 2013

 

Daytime Color Appearance of Retroreflective Traffic Control Sign Materials

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FOREWORD

Retroreflective materials used for street and highway traffic control signs were developed to increase nighttime visibility by reflecting a maximum amount of light back from the headlights of a vehicle to the eyes of a driver. The retroreflective properties of these sign materials increase the variability of photometric measurements taken from the materials both in the laboratory and in the field. In addition, the retroreflective properties of these sign materials may affect their color appearance when viewed by drivers under daylight conditions.

This report describes a research study conducted to determine physical measurements of the chromaticity and luminance of retroreflective sign materials by means of instruments and to determine perceptual measurements of the color appearance (hue, apparent saturation, and brightness) of these materials as judged by a group of human observers. Comparisons are presented between physical measurements made in the laboratory and in the field and between these physical measurements and the psychophysical determination of color appearance obtained from a sample of 17 observers. These comparisons have implications for the specification of allowed color ranges for retroreflective sign materials.

This report will be of interest to Federal, State, and local agencies concerned with specifying and maintaining the color properties of retroreflective traffic control signs, to sign material manufacturers, and to researchers studying the visibility of signs as related to highway safety.

Monique R. Evans
Director, Office of Safety
Research and Development

 

Notice

This document is disseminated under the sponsorship of the U.S. Department of Transportation in the interest of information exchange. The U.S. Government assumes no liability for the use of the information contained in this document. This report does not constitute a standard, specification, or regulation.

The U.S. Government does not endorse products or manufacturers. Trademarks or manufacturers’ names appear in this report only because they are considered essential to the objective of the document.

Quality Assurance Statement

The Federal Highway Administration (FHWA) provides high-quality information to serve Government, industry, and the public in a manner that promotes public understanding. Standards and policies are used to ensure and maximize the quality, objectivity, utility, and integrity of its information. FHWA periodically reviews quality issues and adjusts its programs and processes to ensure continuous quality improvement.

 

Technical Report Documentation Page

1. Report No.

FHWA-HRT-13-018

2. Government Accession No. 3 Recipient's Catalog No.
4. Title and Subtitle

Daytime Color Appearance of Retroreflective Traffic Control Sign Materials

5. Report Date

April 2013

6. Performing Organization Code
7. Author(s)

John A. Molino, Jason F. Kennedy, Pascal A. Beuse, C. Cameron Miller, Wendy Davis, and Carl K. Andersen

8. Performing Organization Report No.

 

9. Performing Organization Name and Address

Science Applications International Corporation (SAIC)
8301 Greensboro Drive
M/S T1-12-3
McLean, VA 22102

10. Work Unit No. (TRAIS)

11. Contract or Grant No.

DTFH61-08-C-00006

12. Sponsoring Agency Name and Address

Federal Highway Administration
Office of Safety Research and Development
Turner-Fairbank Highway Research Center
6300 Georgetown Pike
McLean, VA 22101-2296

13. Type of Report and Period Covered

Final Report, January 2007–May 2010

14. Sponsoring Agency Code

HRDS-05

15. Supplementary Notes

The FHWA Contracting Officer’s Technical Representative (COTR) was Christopher Monk, HRDS-30.

16. Abstract

Photometric measurements of the daytime chromaticity and luminance of retroreflective sign materials were made both in the laboratory and in the field. These instrument measurements were compared with daytime perceptual judgments of color properties made by human observers in the field. Hue, saturation, and brightness were determined for four different types of retroreflective sheeting materials and one diffuse material at four quadrants of each color area for six different colors specified in the Code of Federal Regulations for use on street and highway traffic control signs.

 

Overall, participants’ responses aligned well with the instrument measurements. The introduction of retroreflective properties reduced both the apparent saturation and the brightness of all the colors. The results for the white, green, and blue color areas showed distinct color separations for retroreflective sign materials. The results for the red, orange, and yellow areas showed less color separation but little overlap among contiguous colors in the perceptual color space.

 

This outcome has implications for determining the shape and size of the color areas used to specify the colors that may be employed on traffic control signs. While the present color areas seem to adequately support the daytime perception of the color of retroreflective sign materials for the six colors tested, special attention needs to be paid to the red/orange and orange/yellow color boundaries in any future revisions to the Federal Highway Administration (FHWA) color areas. The results of the present experiment indicate that there is no pressing need to modify the FHWA color areas, but improvements might be made in future iterations so as to enhance separation of those color areas that are more difficult to discriminate.

17. Key Words

Daytime color appearance, Retroreflective signs, Hue scaling, Saturation scaling, Brightness scaling, Color boxes, Chromaticity, Luminance

18. Distribution Statement

No restrictions. This document is available through the National Technical Information Service, Springfield, VA 22161.

19. Security Classification
(of this report)

Unclassified

20. Security Classification
(of this page)

Unclassified

21. No. of Pages

71

22. Price
Form DOT F 1700.7 (8-72) Reproduction of completed page authorized

 

SI* (Modern Metric) Conversion Factors

 

TABLE OF CONTENTS

CHAPTER 1. INTRODUCTION

CHAPTER 2. METHODOLOGY

CHAPTER 3. RESULTS

CHAPTER 4. SUMMARY AND DISCUSSION

APPENDIX A. PARTICIPANT MATERIALS

APPENDIX B. PHYSICAL MEASUREMENTS

APPENDIX C. HUMAN PSYCHOPHYSICAL RESULTS

ACKNOWLEDGEMENTS

REFERENCES

 

LIST OF LIST OF FIGURES

Figure 1. Graph. FHWA daylight chromaticity coordinates for various colors of retroreflective materials plotted in the CIE 1931 color space
Figure 2. Graph. CIE daylight chromaticity coordinates for various colors of retroreflective materials plotted in the CIE 1931 color space
Figure 3. Graph. CIE 1931 x, y chromaticity diagram
Figure 4. Illustration. CIELAB color space
Figure 5. Illustration. Plan view of the experimental setup (not to scale)
Figure 6. Photo. Standard retroreflective STOP sign in a typical application
Figure 7. Photo. Outdoor experiment setup on the grounds of TFHRC
Figure 8. Graph. Mean laboratory (PR-715) and field (PR-650) physical color measurements of the white diffuse reflector with color filters
Figure 9. Graph. Mean laboratory (PR-715) and field (PR-650) physical color measurements averaged over four retroreflective sheeting types
Figure 10. Graph. Laboratory (LabScan® XE) physical color measurements averaged over four retroreflective sheeting types
Figure 11. Graph. Laboratory (PR-715) physical color measurements of four retroreflective sheeting types
Figure 12. Graph. Field (PR-650) physical color measurements of four retroreflective sheeting types
Figure 13. Graph. Individual field chromaticity measurements for the diffuse white standard reflector
Figure 14. Graph. Mean perceptual color ratings for the white diffuse reflector with color filters for 17 participants
Figure 15. Graph. Mean perceptual color ratings averaged over four retroreflective sheeting types for 17 participants
Figure 16. Graph. Mean perceptual color ratings of four sheeting types
Figure 17. Graph. Mean hue angle in radians with 95 percent confidence limit of two standard errors
Figure 18. Graph. Mean field luminance measurements by sheeting type for all colors
Figure 19. Graph. Mean field luminance measurements of the yellow and red samples used for the brightness ranking task
Figure 20. Graph. Mean brightness ratings by sheeting type for all colors
Figure 21. Graph. Mean brightness rankings for yellow and red samples
Figure 22. Graph. Mean brightness rating as a function of mean luminance for six colors
Figure 23. Graph. Mean brightness rating as a function of mean lightness (L*) for six colors
Figure 24. Illustration. Training examples for saturation
Figure 25. Illustration. Training examples for brightness
Figure 26. Illustration. Example participant practice sample
Figure 27. Illustration. Color dimensions
Figure 28. Illustration. Response sheet sample
Figure 29. Graph. Laboratory (LabScan® XE) physical color measurements of four retroreflective sheeting types
Figure 30. Graph. Comparison of mean field (PR-650) physical color measurements from 2007 and 2008 averaged over four retroreflective sheeting types
Figure 31. Graph. Mean perceptual color ratings for type VIII sheeting for 17 participants
Figure 32. Graph. Mean color ratings for type VIII sheeting for participant 1
Figure 33. Graph. Mean color ratings for type VIII sheeting for participant 2
Figure 34. Graph. Mean color ratings for type VIII sheeting for participant 3
Figure 35. Graph. Mean color ratings for type VIII sheeting for participant 4
Figure 36. Graph. Mean color ratings for type VIII sheeting for participant 5
Figure 37. Graph. Mean color ratings for type VIII sheeting for participant 6
Figure 38. Graph. Mean color ratings for type VIII sheeting for participant 7
Figure 39. Graph. Mean color ratings for type VIII sheeting for participant 8
Figure 40. Graph. Mean color ratings for type VIII sheeting for participant 9
Figure 41. Graph. Mean color ratings for type VIII sheeting for participant 10
Figure 42. Graph. Mean color ratings for type VIII sheeting for participant 11
Figure 43. Graph. Mean color ratings for type VIII sheeting for participant 12
Figure 44. Graph. Mean color ratings for type VIII sheeting for participant 13
Figure 45. Graph. Mean color ratings for type VIII sheeting for participant 14
Figure 46. Graph. Mean color ratings for type VIII sheeting for participant 15
Figure 47. Graph. Mean color ratings for type VIII sheeting for participant 16
Figure 48. Graph. Mean color ratings for type VIII sheeting for participant 17

 

LIST OF TABLES

Table 1. Participant characteristics by age and gender category
Table 2. Typical daily experimental schedule
Table 3. Paired comparison t-tests for hue angles
Table 4. Paired comparison t-tests for brightness ratings

 

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