Visual Detection of Detectable Warning Materials by Pedestrians with Visual Impairments - Final Report

3.1 Key Findings

• There were many combinations of detectable warning color and sidewalk color that were seen from a distance of 2.44 m (8 ft) by pedestrians with visual impairments, but there were fewer combinations seen from 7.92 m (26 ft) and fewer that were rated highly in their ability to attract pedestrians’ attention. Forty-one of the 52 combinations tested were seen by more than 85 percent of the participants from 2.44 m (8 ft), 14 of 52 combinations were seen by more than 85 percent of participants from 7.92 m (26 ft), and only 3 of the combinations received high conspicuity ratings from more than 85 percent of the participants.

• Detectable warnings that are the same color as the sidewalk or very similar in color to the sidewalk could not be seen by most participants in this study.

• For most detectable warning colors tested, the color of the sidewalk upon which the detectable warning was placed influenced how easily it could be seen. An exception to this was the high contrast black-and-white patterned detectable warnings which were generally detectable and conspicuous across all four sidewalk types.

• The luminance contrast between the detectable warning and sidewalk (particularly the logarithm of contrast) was an important factor for predicting the percentage of participants with visual impairments who were able to see the detectable warning. At contrasts above 70 percent, detectable warnings were seen from 2.44 m (8 ft) by approximately 95 percent of the participants. At contrasts above 50 percent, more than 90 percent of participants were able to see the detectable warning at 2.44 m (8 ft). The only exception to this was the black detectable warning on the asphalt sidewalk which had a dark-on-light contrast of 68 percent. It was seen by fewer than 80 percent of the participants.

• Regression analyses show that in addition to luminance contrast, other factors may be important predictors of visual detection and conspicuity for detectable warnings. In particular, there were differences between chromatic and achromatic detectable warnings. The four red and yellow detectable warnings (bright red, orange-red, federal yellow, and pale yellow) generally provided greater conspicuity and greater probability of detection than achromatic detectable warnings for a given level of luminance contrast. For predicting high conspicuity ratings the reflectance of the detectable warning is helpful. Based on parameter estimates for the regression models, having lighter detectable warnings (higher reflectance) predicts high conspicuity ratings.

• Regression analyses show no evidence that the range of lighting conditions (cloud cover, illuminance) tested in this study influence detection or conspicuity of detectable warnings.

• Participants’ descriptions of detectable warning colors sometimes changed with sidewalk type, although most color descriptions given were consistent with the perceptions of the experimenters (who had no visual impairment). Some participants’ use of color names was clearly inconsistent with other participants’ descriptions, indicating variability in color perception for detectable warnings.

• Participants’ unsolicited comments about the suitability of various detectable warnings were recorded and are included in Appendix G. Some of the comments focused on the problem that certain detectable warnings may look like other things commonly encountered on sidewalks such as holes, patches, or debris.