Nighttime Visibility of Traffic Signs: 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.

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.

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.

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.

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.