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                APPENDIX D - 1993 AND 1998 MINIMUM RETROREFLECTIVITY RESEARCH RECOMMENDATIONS
As described in the first chapter, the FHWA first published research recommendations for minimum levels of in-service retroreflectivity in 1993 (8). These retroreflectivity levels were later updated in a 1998 research report (10). Both sets of retroreflectivity levels represent research recommendations and neither has been proposed in any previous rulemaking effort. The 1998 minimum levels of in-service retroreflectivity are presented in Tables 7 through 10. The retroreflectivity levels shown in parenthesis are those recommended in the original 1993 research report, if the levels are different from the 1998 values. If there are no values in parenthesis, the 1998 levels did not change from the 1993 values.

Table 7. 1998 Minimum Retroreflectivity Values for White Regulatory and Guide Signs
	**Legend Color**
			**Black and/or Red****Background Color**
			**White****Traffic Speed**
			45 mph or greater
			40 mph or less**Sign Size**
			> 48 in
			30-36 in
			< 24 in
			> 48 in
			30-36 in
			< 24 in**Material Type**
			**Minimum Retroreflectivity Values (cd/lux/m2)1**Type I (EG)
			25 (20)
			35
			45 (50)
			20 (15)
			25 (20)
			30 (35)Type II (SEG)
			30 (25)
			45
			55 (70)
			25 (20)
			30
			35 (55)Type III (HI)
			40 (30)
			55 (60)
			70 (90)
			30 (25)
			40 (45)
			45 (75)Type IV & VII (Prismatic)
			50 (40)
			70 (80)
			90 (120)
			40 (35)
			50 (60)
			60 (100)Note:    Parking series signs and signs intended solely for pedestrians and bicyclists are not included in this category.

Values in parenthesis are the original 1993 values, if different from the 1998 values.

1Measured at an entrance angle of -4.0 degrees and an observation angle of 0.2 degrees.



Table 8. 1998 Minimum Retroreflectivity Values for Yellow and Orange Warning Signs
	**Legend Color**
			**Black****Background Color**
			**Yellow or Orange****Type of Legend**
			**Material Type**
			**Minimum Retroreflectivity Values (cd/lux/m2)1****Sign size****> 48 in**
			**Sign size = 36 in**
			**Sign size****< 30 in**Bold Symbol2
			ALL
			15
			20
			25Fine Symbol
			& Word3
			Type I (EG)
			20
			30
			35 (45)Type II (SEG)
			25
			35 (40)
			45 (60)Type III (HI)
			30
			45 (50)
			55 (80)Type IV & VII (Prismatic)
			40
			60 (70)
			70 (120)Note:    Values in parenthesis are the original 1993 values, if different from the 1998 values.

1Measured at an entrance angle of -4.0 degrees and an observation angle of 0.2 degrees.

2Warning signs with bold symbols include: Turn (W1-1), Curve (W1-2), Reverse Turn (W1-3), Reverse Curve (W1-4), Winding Road (W1-5), Large Arrow (W1-6), Double Head Arrow (W1-7), Chevron  (W1-8), Cross Road (W2-1), Side Road (W2-2), T Intersection (W2-4), Y Intersection (W2-5), Stop Ahead (W3-1a), Yield Ahead (W3-2a), Signal Ahead (W3-3), Merge (W4-1), Lane Reduction (W4-2), Added Lane (W4-3), Divided Highway Begins (W6-1), Divided Highway Ends (W6-2), Two-Way Traffic (W6-3), Slippery When Wet (W8-5), Advance Pedestrian Crossing (W11-2), Pedestrian Crossing (W11A-2), Flagger Ahead (W20-7a).

3Fine Symbol and Word Signs include all other black on yellow or orange warning signs.

Table 9. 1998 Minimum Retroreflectivity Guidelines for Green Guide Signs
	**Legend Color**
			**White****Background Color**
			**Green****Traffic Speed**
			45 mph or greater
			40 mph or less**Color**
			White
			Green
			White
			Green**Sign Position**
			**Minimum Retroreflectivity Values (cd/lux/m2)1**Ground-Mounted
			35
			7
			25
			5Note:    Values in parenthesis are the original 1993 values, if different from the 1998 values.

1Measured at an entrance angle of -4.0 degrees and an observation angle of 0.2 degrees.



Table 10. 1998 Minimum Retroreflectivity Values for Red Regulatory Signs
	**Legend Color**
			**White****Background Color**
			**Red****Traffic Speed**
			45 mph or greater
			40 mph or less**Sign Size**
			> 48 in
			36 in
			< 30 in
			> 48 in
			36 in
			< 30 in**Portion of Sign**
			White
			Red
			White
			Red
			White
			Red
			White
			Red
			White
			Red
			White
			Red**Minimum Retroreflectivity Values (cd/lux/m2)1**
			35

			(50)
			8

			(10)
			45

			(60)
			8

			(12)
			50

			(70)
			8

			(14)
			25

			(30)
			5

			(6)
			30

			(35)
			5

			(7)
			35

			(40)
			5

			(8)Note:    White on red signs include: Stop (R1-1), Yield (R1-2), Do Not Enter (R5-1), and Wrong Way (R5-1a).

Values in parenthesis are the original 1993 values, if different from the 1998 values.

1Measured at an entrance angle of -4.0 degrees and an observation angle of 0.2 degrees. Since both the legend and the background of these signs are retroreflectorized, a minimum maintained contrast ratio of 4:1 has also been established. If the retroreflectivity value for either the white or red material falls below the value specified in the table or the retroreflectivity of the white material divided by the retroreflectivity of the red material is less than four, the sign should be replaced.
      
  Book traversal links for APPENDIX D - 1993 AND 1998 MINIMUM RETROREFLECTIVITY RESEARCH RECOMMENDATIONS
      ‹ APPENDIX C - SUMMARY OF 1995 WORKSHOPS
                    Up
                    APPENDIX E - AASHTO POLICY RESOLUTION ›
                
                Book:Workshops on Nighttime Visibility of Traffic Signs: Summary of Workshop Findings
              CHAPTER 1 - INTRODUCTION
                CHAPTER 2 - NIGHT RETROREFLECTIVITY DEMONSTRATION
                CHAPTER 3 - SUMMARY OF FINDINGS
                CHAPTER 4 - RECOMMENDATIONS
                CHAPTER 5 - REFERENCES
                APPENDIX A - MUTCD RETROREFLECTIVITY HISTORY
                APPENDIX B - RETROREFLECTIVITY ADVANCE NOTICE
                APPENDIX C - SUMMARY OF 1995 WORKSHOPS
                APPENDIX D - 1993 AND 1998 MINIMUM RETROREFLECTIVITY RESEARCH RECOMMENDATIONS
                APPENDIX E - AASHTO POLICY RESOLUTION
                APPENDIX F - WORKSHOP PARTICIPANTS
                APPENDIX G - ORGANIZATIONS' RETROREFLECTIVITY POLICIES
                APPENDIX H - WORKSHOP MUTCD LANGUAGE
                APPENDIX I - QUESTIONS TO BE CONSIDERED U.S. DEPARTMENT OF TRANSPORTATION

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