FHWA Standards


 

    ASTM Designations Define Performance Levels

    ASTM designations define sheeting by type, from engineering grade beaded type to microprismatics. These specifications support consistent, standardized enhancements of sign visibility.

    Recognize measurement guidelines and issues(15)

    ASTM is likely the most familiar source for procedures for measuring retroreflectivity (although several states have developed their own specifications). Common ASTM procedures for measuring the retroreflectivity of signs in the field include:
    • E808 (Standard Practice for Describing Retroreflection)
    • E809 (Standard Practice for Measuring Photometric Characteristics of Retro reflectors)
    • E810 (Standard Test method for Coefficient of Retroreflection for Retroreflective Sheeting)
    • E1709 (Standard Test Method for Measurement of Retroreflective Signs Using a Portable Retroreflectometer)
    Most agencies use ASTM D4956 to establish minimum retroreflectivity and color performance requirements for new sheeting. The specification contains several tables (the example shows Type III) that provide minimum retroreflectivity values at different observation and entrance angles for each color.



    (Image source: 15)

    Notice of Proposed Amendment: Maintaining Traffic Sign Retroreflectivity Presentation

    Legibility tests of overhead signs using passenger car and SUV-type vehicles across different age groups indicated ASTM Type IX retroreflective sheeting provided statistically longer legibility distances than Type III sheeting, averaging 9.5% improvement.(19)

    Recent Minnesota Department of Transportation (MnDOT) side-by-side comparisons of stop signs indicated that new product was brighter than MnDOT’s existing sheeting, causing the agency to specify new sheeting material on all new sign placements.(20) Independent traffic studies conclude that 100% replacement is an effective strategy for reducing the percentage of non-compliant signs.(15)
    • All sign colors --- red, yellow, white and green --- fall within FHWA minimum retroreflectivity standards.
    • ASTM (American Society of Testing and Materials) designations set retroreflectivity industry standards to define types and performance levels for new sheeting.(15)
    • There is clear evidence that upgrading signs from Type I to Type III and or Type IX reflective sheeting improves safety with a positive benefit-to-cost ratio.(16, 17)
    15 Traffic sign retroreflectivity "sign retro 101", FHWA Visibility Team PowerPoint
    16 Harris, E.A., et al, Analysis of traffic sign asset management scenarios, TRB 2007 Annual Meeting CD-ROM
    17 Ripley, D.A., Quantifying the safety benefits of traffic control devices—benefit—cost analysis of traffic sign upgrades, 2005 Mid-Continent Transportation Research Symposium Proceedings
    18 Carlson, P.E., Legibility of overhead guide signs using encapsulated versus microprismatic retroreflective sheeting, TRB 16th Biennial Visibility Symposium, June 2002
    20 Stutts, J., Gearing up for an aging population, Public Roads Magazine, May/June 2006
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