Methods for Maintaining Traffic Sign Retroreflectivity

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November 2007
Publication No. FHWA-HRT-08-026

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Foreword

Signs are considered essential to communicating regulatory, warning, and guidance information. It is critical that signs are able to fulfill this role during both daytime and nighttime periods. The ability of a sign to fulfill its role during nighttime periods is provided by a unique form of reflection known as "retroreflectivity." The retroreflectivity of signs, however, degrades as the signs age in the field. A new standard in the Manual on Uniform Traffic Control Devices (MUTCD) requires that agencies maintain traffic signs to a minimum level of retroreflectivity. Various methods can be used within an agency's sign management processes to meet and maintain a minimum retroreflectivity requirement for traffic signs. This report describes methods for maintaining traffic sign retroreflectivity that can be used by agencies to:

  • Systematically identify those signs that do not meet the minimum level of retroreflectivity.
  • Initiate activities that will upgrade signs that fall below the minimum required levels.
  • Monitor the retroreflectivity of in-place signs.
  • Create procedures that will assess the need to change practices and policies to enhance the nighttime visibility of signs.

It is not appropriate to prescribe a single detailed method for all agencies to follow. The most cost effective and efficient method to maintain sign retroreflectivity will vary by agency, depending on the types of signs in service and the traffic and environmental conditions. Therefore, this report outlines several possible methods an agency can employ to maintain a minimum level of traffic sign retroreflectivity.

Michael F. Trentacoste
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 document 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.


Form DOT F 1700.7 (8-72)

1. Report No.
FHWA-HRT-08-026
2. Government Accession No. 3. Recipient's Catalog No.
4. Title and Subtitle
Methods for Maintaining Traffic Sign Retroreflectivity
5. Report Date
November 2007
6. Performing Organization Code
7. Author(s)
Paul J. Carlson and Matt S. Lupes
8. Performing Organization Report No.
9. Performing Organization Name and Address
Texas Transportation Institute
The Texas A&M University System
College Station, TX 77843-3135
10. Work Unit No.
11. Contract or Grant No.
Project No. 474840
12. Sponsoring Agency Name and Address

Office of Safety Research and Development
Federal Highway Administration
6300 Georgetown Pike
McLean, VA 22101-2296
13. Type of Report and Period Covered
Final Report, March 2003–June 2005
14. Sponsoring Agency Code
15. Supplementary Notes
Research performed in cooperation with the U.S. Department of Transportation and the Federal Highway Administration.
Project Contracting Officer's Technical Representative: Kenneth S. Opiela
Turner-Fairbank Highway Research Center Safety Research and Development (HRDS-5)
Federal Highway Administration (HSA-10)
16. Abstract
In response to a Congressional directive, the FHWA has established minimum maintained traffic sign retroreflectivity levels that are incorporated into the Manual on Uniform Traffic Control Devices (MUTCD). One of the concerns expressed by agency personnel responsible for being in conformance with required minimums is the potential increase in tort exposure. The FHWA has developed retroreflectivity maintenance methods that, when implemented as intended, provide agencies with a flexible means of being in conformance with required minimum retroreflectivity levels and provide protection from potential tort claims. Other properly supported methods (i.e., through the completion of an engineering study) may be used to maintain signs at the required minimum retroreflectivity levels. Agencies can use the information in this report to help determine which retroreflectivity maintenance method or combination of methods best suits their needs.
17. Key Words
RETROREFLECTIVITY, TRAFFIC CONTROL DEVICES, TRAFFIC SIGNS, RETROREFLECTIVE SHEETING MATERIAL, SIGN MAINTENANCE, MINIMUM RETROREFLECTIVITY, RETROREFLECTOMETER
18. Distribution Statement
No restrictions. This document is available to the public through:
National Technical Information Service
5285 Port Royal Road
Springfield, VA 22161
19. Security Classif.
(of this report)

Unclassified
20. Security Classif.
(of this page)

Unclassified
21. No. of Pages
47
22. Price

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


SI* (MODERN METRIC) CONVERSION FACTORS

APPROXIMATE CONVERSIONS TO SI UNITS
Symbol When You Know Multiply By To Find Symbol
LENGTH
in inches 25.4 millimeters mm
ft feet 0.305 meters m
yd yards 0.914 meters m
mi miles 1.61 kilometers km
AREA
in2 square inches 645.2 square millimeters mm2
ft2 square feet 0.093 square meters m2
yd2 square yard 0.836 square meters m2
ac acres 0.405 hectares ha
mi2 square miles 2.59 square kilometers km2
VOLUME
fl oz fluid ounces 29.57 milliliters mL
gal gallons 3.785 liters L
ft3 cubic feet 0.028 cubic meters m3
yd3 cubic yards 0.765 cubic meters m3
NOTE: volumes greater than 1000 L shall be shown in m3
MASS
oz ounces 28.35 grams g
lb pounds 0.454 kilograms kg
T short tons (2000 lb) 0.907 megagrams (or "metric ton") Mg (or "t")
TEMPERATURE (exact degrees)
°F Fahrenheit 5 (F-32)/9 or (F-32)/1.8 Celsius °C
ILLUMINATION
fc foot-candles 10.76 lux lx
fl foot-Lamberts 3.426 candela/m2 cd/m2
FORCE and PRESSURE or STRESS
lbf poundforce 4.45 newtons N
lbf/in2 poundforce per square inch 6.89 kilopascals kPa

APPROXIMATE CONVERSIONS FROM SI UNITS
Symbol When You Know Multiply By To Find Symbol
LENGTH
mm millimeters 0.039 inches in
m meters 3.28 feet ft
m meters 1.09 yards yd
km kilometers 0.621 miles mi
AREA
mm2 square millimeters 0.0016 square inches in2
m2 square meters 10.764 square feet ft2
m2 square meters 1.195 square yards yd2
ha hectares 2.47 acres ac
km2 square kilometers 0.386 square miles mi2
VOLUME
mL milliliters 0.034 fluid ounces fl oz
L liters 0.264 gallons gal
m3 cubic meters 35.314 cubic feet ft3
m3 cubic meters 1.307 cubic yards yd3
MASS
g grams 0.035 ounces oz
kg kilograms 2.202 pounds lb
Mg (or "t") megagrams (or "metric ton") 1.103 short tons (2000 lb) T
TEMPERATURE (exact degrees)
°C Celsius 1.8C+32 Fahrenheit °F
ILLUMINATION
lx lux 0.0929 foot-candles fc
cd/m2 candela/m2 0.2919 foot-Lamberts fl
FORCE and PRESSURE or STRESS
N newtons 0.225 poundforce lbf
kPa kilopascals 0.145 poundforce per square inch lbf/in2

*SI is the symbol for the International System of Units. Appropriate rounding should be made to comply with Section 4 of ASTM E380. (Revised March 2003)


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Program Contact

Cathy Satterfield

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