ASTM_D_8379_-_D_8379M_-_21.pdf

Designation:D8379/D8379M21Standard Practice forEvaluating Nighttime Retroreflective Sheeting EffectivenessUsing Positive-Contrast Textual Sign Scenario PerformanceAnalysis1This standard is issued under the fixed designation D8379/D8379M;the number immediately following the designation indicates theyear of original adoption or,in the case of revision,the year of last revision.A number in parentheses indicates the year of lastreapproval.A superscript epsilon()indicates an editorial change since the last revision or reapproval.1.Scope1.1 This practice provides a framework to evaluate retrore-flective sheeting performance in nighttime driving conditionswithout a need for field evaluations through a set of signviewing scenarios representing common use-cases.The evalu-ation of performance of a specific sheeting is achieved bycomparing the luminance provided by a sheeting to theluminance needed by drivers in each scenario.This comparisonis expressed in terms of a“Performance Index,”which is ameasure for how well the luminance provided to the drivermeets their needs,in each of the scenarios.Comparison of theperformance index values for different sheeting allows the userto predict differences in nighttime retroreflective performancewhen those sheeting are used on installed signs.1.2 The driver-needs data is based on textual signs(not onsymbolic signs)with positive contrast(sign text being brighterthan its background),and the headlamp illumination is as-sumed to be low-beams;therefore,performance index isapplicable only to textual signs viewed under low-beamheadlamp illumination.1.3 UnitsThe values stated in either SI units or inch-pound units are to be regarded separately as standard.Thevalue stated in each system may not be exact equivalents;therefore,each system shall be used independently of the other.Combining values from the two systems may result in noncon-formance with the standard.1.4 This standard does not purport to address all of thesafety concerns,if any,associated with its use.It is theresponsibility of the user of this standard to establish appro-priate safety,health,and environmental practices and deter-mine the applicability of regulatory limitations prior to use.1.5 This international standard was developed in accor-dance with internationally recognized principles on standard-ization established in the Decision on Principles for theDevelopment of International Standards,Guides and Recom-mendations issued by the World Trade Organization TechnicalBarriers to Trade(TBT)Committee.2.Referenced Documents2.1 ASTM Standards:2B209/B209M Specification for Aluminum and Aluminum-Alloy Sheet and PlateB449 Specification for Chromates on AluminumD8 Terminology Relating to Materials for Roads and Pave-mentsE284 Terminology of AppearanceE808 Practice for Describing RetroreflectionE809 Practice for Measuring Photometric Characteristics ofRetroreflectors2.2 BSI Standard:3BS 8408:2005 Road Traffic Signs.Testing and Performanceof Microprismatic Retroreflective Sheeting Materials.Specification(Withdrawn)3.Terminology3.1 DefinitionsFor definitions of technical terms used inthis practice,see Terminologies D8 and E284.3.2 Definitions of Terms Specific to This Standard:3.2.1 legibility index,na surrogate metric for the size ofthe image on the retina,expressed in terms of the longitudinal(roadway)distance to the sign divided by the height of theuppercase alphanumeric on the text.3.2.2 legibility range,nthe range of distances to a sign,expressed longitudinally along the roadway centerline,that arebetween a legibility index of 40 ft/in.4.8 m/cm and 20 ft/in.2.4 m/cm.3.2.3 performance index,na measure that approximates asign sheetings performance,in terms of luminance observedby the driver,in a given scenario.1This practice is under the jurisdiction of ASTM Committee D04 on Road andPaving Materials and is the direct responsibility of Subcommittee D04.38 onHighway Traffic Control Materials.Current edition approved Nov.1,2021.Published December 2021.DOI:10.1520/D8379_D8379M-21.2For referenced ASTM standards,visit the ASTM website,www.astm.org,orcontact ASTM Customer Service at serviceastm.org.For Annual Book of ASTMStandards volume information,refer to the standards Document Summary page onthe ASTM website.3Available from British Standards Institution(BSI),389 Chiswick High Rd.,London W4 4AL,U.K.,http:/.Copyright ASTM International,100 Barr Harbor Drive,PO Box C700,West Conshohocken,PA 19428-2959.United StatesThis international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for theDevelopment of International Standards,Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade(TBT)Committee.1?3.2.4 RAmultiplier,na factor derived from the illuminanceat the sign per headlight,measured facing the headlight in ascenario,while also incorporating windshield transmission andthe cosine of viewing angle.3.2.4.1 D