U.S. Department of Transportation
Federal Highway Administration
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Federal Highway Administration Research and Technology
Coordinating, Developing, and Delivering Highway Transportation Innovations
| REPORT |
| This report is an archived publication and may contain dated technical, contact, and link information |
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| Publication Number: FHWA-HRT-13-018 Date: April 2013 |
Publication Number: FHWA-HRT-13-018 Date: April 2013 |
PDF files can be viewed with the Acrobat® Reader®
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 |
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| 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.
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9. Performing Organization Name and Address Science Applications International Corporation (SAIC) |
10. Work Unit No. (TRAIS) |
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11. Contract or Grant No. DTFH61-08-C-00006 |
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12. Sponsoring Agency Name and Address Federal Highway Administration |
13. Type of Report and Period Covered
Final Report, January 2007–May 2010 |
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14. Sponsoring Agency Code HRDS-05 |
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15. Supplementary Notes The FHWA Contracting Officer’s Technical Representative (COTR) was Christopher Monk, HRDS-30. |
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| 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. |
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| 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. |
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19. Security Classification Unclassified |
20. Security Classification 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
CHAPTER 4. SUMMARY AND DISCUSSION
APPENDIX A. PARTICIPANT MATERIALS
APPENDIX B. PHYSICAL MEASUREMENTS
APPENDIX C. HUMAN PSYCHOPHYSICAL RESULTS
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
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
