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Federal Highway Administration Research and Technology
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This report is an archived publication and may contain dated technical, contact, and link information |
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Publication Number: FHWA-RD-03-082
Date: December 2003 |
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Minimum Retroreflectivity Levels for Overhead Guide Signs and Street-Name SignsPDF Version (837 KB)
PDF files can be viewed with the Acrobat® Reader® U.S. Department of Transportation Federal Highway Administration Research, Development, and Technology Office of Safety Research and Development Turner-Fairbank Highway Research Center 6300 Georgetown Pike McLean, Virginia 22101 ForewordReport FHWA-RD-03-082 presents the results of a study that investigated the nighttime visibility needs of drivers for viewing overhead guide signs and street name signs. This effort reviewed past research and current practices to design a series of field tests. Field experiments were conducted with drivers 55 years and older in which the headlight illumination was incrementally increased until they could correctly read the messages on the overhead signs. The results from these experiments provided the data needed to determine threshold levels of demand luminance necessary to meet driver needs. The researchers back calculated minimum sign retroreflectivity levels using information about the supply luminance associated with the various retroreflective sign materials and amounts of illumination provided. The research indicated that some combinations of sign materials were inadequate to meet driver needs given changes in the headlight design, legibility requirements, viewing position from larger vehicles, and other factors. Tables of recommended minimum retroreflectivity levels for overhead guide and street name signs were formulated from the data gathered in the research. These tables cover a subset of signs that had not been addressed in previous research. It is important to note that this research was initially completed before the need for updates to the other previously developed tables of minimum levels of traffic sign retroreflectivity became apparent. Subsequently, another research effort was undertaken to determine the factors needing updating and to generate new tables. Following that updating effort, the contractor for this project reanalyzed the minimum levels for overhead guide and street name signs using updated inputs for vehicle dimensions, headlight characteristics, driver age, material performance, legibility, and other factors. The revised set of the tables for minimum retroreflectivity for overhead guide and street name signs is provided in Chapter 8 of this report. Sufficient copies of this report have been produced to allow distribution to FHWA division offices, resources centers and each state highway agency. Copies can be requested from the FHWA Office of Safety or the Office of Safety R&D. In addition, this report is available on-line through the FHWA electronic library at http://www.fhwa.dot.gov/research/tfhrc/programs/safety/index.cfm. Michael Trentacoste Director, Office of Safety R&D Notice: This document is disseminated under the sponsorship of the Department of Transportation in the interest of information exchange. The United States Government assumes no liability for the contents or the use thereof. The report does not constitute a standard, specification, or regulation. The United States Government does not endorse products or manufacturers. Trade and manufacturers’ names appear in this report because they are considered essential to the object of the document. Technical Report Documentation Page
Form DOT F 1700.7 (8-72) Reproduction of completed page authorized CHAPTER 7. INITIAL RECOMMENDATIONS APPENDIX A. SURVEY OF CURRENT PRACTICES
Figure 1. Questions Included in Transportation Agency E-Mail Survey Figure 2. Weathering Degradation of Retroreflective Sheeting Figure 3. Overhead Sign Retroreflectivity Values Figure 4. Layout of Overhead Sign Panel and Legend Figure 5. Supplied Legend Luminance Graphs Figure 6. Ford Taurus Headlamp Output Figure 10. Use of Laser for Aiming Figure 12. Chromaticity Color Shift (CIE, 1931) Figure 13. Closeup Chromaticity Color Shift (CIE, 1931) Figure 14. Color Temperature Shift Figure 18. Overhead Sign Results Figure 19. Street-Name Sign Results Figure 20. Results for Overhead Signs Figure 21. Results for Street-Name Signs Figure 22. Isocandela Plots of CARTS50 (Top) and UMTRI25PC Headlamp Figure 23. E-mail Survey Sent to State and Local Transportation Agencies LIST OF TABLES Table 2. Types of Retroreflective Sheeting Table 3. Sign Dimension Conversions. Table 4. Replacement Luminance Values. Table 5. Recommended SIA Values for Green Background Areas of Overhead Guide Signs. Table 7. MR Guidelines for Signs with Green Backgrounds. Table 8. Headlamp and Driver's Eye Height Table 9. List of Transportation Agencies That Responded. Table 10. State Agency Responses to Overhead Sign Questions. Table 11. Local Agency Responses to Overhead Sign Questions. Table 12. State Agency Responses to Street-Name Sign Questions. Table 13. Local Agency Responses to Street-Name Sign Questions. Table 14. Average RA of New White Sheeting. Table 16. Supplied Legend Luminance Values (cd/m2) Table 17. Subject Information. Table 18. Threshold Luminance Values by Accommodation Level (cd/m2) Table 19. Replacement Luminance Values. Table 20. Initial MR Levels for Overhead Guide Signs (50-Percent Accommodation) Table 21. Initial MR Levels for Post-Mounted Street-Name Signs (50-Percent Accommodation) Table 22. Initial MR Levels for Overhead Street-Name Signs (50-Percent Accommodation) Table 23. Comparison of Headlamp Profiles for Overhead Signs. Table 24. Comparison of Headlamp Profiles For Right-Shoulder-Mounted Signs. Table 25. Comparison of Headlamp Profiles for Left-Shoulder-Mounted Signs. Table 26. Roadway Illuminance Measurements (in lux) Table 27. Comparison of Specific Vehicles. Table 28. Illuminance Data for Left-Shoulder-Mounted Signs. Table 29. Minimum Overhead Retroreflectivity Levels (50-Percent Accommodation) Table 31. Vehicle Impacts on Overhead Guide Sign MR Levels. Table 32. Average RA of New Unweathered Sheeting. Table 33. Overhead Guide Signs. Table 34. Post-Mounted Street-Name Signs. Table 35. Overhead Street-Name Signs. Table 36. Updated Vehicle Dimensions. Table 37. Initial MR Levels for Overhead Guide Signs(cd/lx/m2) Table 38. Assumed Characteristics and Criteria for Street-Name Signs. Table 39. Initial MR Levels for Street-Name Signs (cd/lx/m2) Table 40. Research Recommendations for Updated MR Levels. Table 41. Overhead Sign Example. |