LEGIBILITY DISTANCES OF FLUORESCENT TRAFFIC SIGNS AND THEIR NORMAL COLOR COUNTERPARTS Paper Number 0

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LEGIBILITY DISTANCES OF FLUORESCENT TRAFFIC SIGNS
AND THEIR NORMAL COLOR COUNTERPARTSPaper Number
01-2417

• Thomas Schnell
• Director
• Operator Performance Laboratory
• Department of Industrial Engineering
• 4135 Seamans Center
• The University of Iowa
• Iowa City, IA 52242-1527

Keith Bentley, Elizabeth Hayes, and Martin
Rick Undergraduate Students Department of
Industrial Engineering The University of
Iowa Iowa City, Iowa 52242-1527
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Introduction

• Fluorescent colors are known to attract driver
  attention
• Attention getting quality of fluorescent colors
  especially pronounced during overcast or
  inclement weather daytime and twilight
• Fluorescent colors are better detected and
  recognized (color classified) than normal colors
  at large angles of eccentricity in the visual
  periphery
• Goal of present study
• Determine the legibility distances of fluorescent
  and non-fluorescent traffic sign materials
• Hypothesis
• Adding the property of fluorescence significantly
  increases the legibility distances

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Literature

• A sound technical description of the working
  principle of durable fluorescent traffic sign
  materials is given by Burns and Pavelka, Color
  Research and Application, Vol. 20, No.2, Apr 1995
• Zwahlen and Schnell (TRR 1605, 1997) investigated
  daytime conspicuity
• fluorescent and non-fluorescent targets
• seen against a green background
• peripheral viewing angle and target size were
  varied
• Brekke and Jenssen (Proceedings of the 1997
  Progress in Automobile Lighting Symposium)
• a study investigating the visibility distances of
  fluorescent and non-fluorescent signs

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Method

• Daytime viewing, field setting
• Dynamic driver observation (legibility) task
• Total of six diamond signs
• One side fluorescent color, other side
  non-fluorescent color
• Landolt Rings were used as legend
• Subjects job was to detect the orientation of
  the Landolt ring
• A PLANT ENTRANCE warning sign was also used for
  base line comparison purposes with previous work
  performed by Zwahlen and Schnell
• A pedestrian symbol warning sign was used as well

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Subjects

• Nine young and healthy subjects
• 6 males, 3 females
• All subjects had a valid US drivers license
• Normal or better visual acuity
• Normal or better contrast sensitivity
• No color perception deficiencies
• The subjects were instructed to verbally
  indicate
• The first point in time the orientation of the
  Landolt ring opening was clearly discernible
• The PLANT ENTRANCE legend was clearly legible
• The pedestrian symbol was clearly recognizable
• Guessing was discouraged
• Resulting from this method are functional
  legibility distances

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Subjects, Adequacy and Limitations

• The subject sample is quite homogenous
• With three replications, we are confident that
  the sample is adequate from a statistical point
  of view
• high statistical power in the Analysis of
  Variance (ANOVA) of 0.99 and 1.0 for fluorescence
  and color, respectively
• However, we are aware that our subject sample
  does not fully represent the licensed driver
  population as a whole

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Sign 1

• Black Paint Landolt C on Yellow Micro prismatic
• Side 1 Normal Yellow
• Side 2 Fluorescent Yellow Green
• Figure shows Fluorescent Yellow Green as Example

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Sign 2

• Black Paint Landolt C on Yellow Micro prismatic
• Side 1 Normal Yellow
• Side 2 Fluorescent Yellow
• Figure shows Normal Yellow as Example

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Sign 3

• Black Paint Landolt C on Pink
• Side 1 Non-Reflective Pink Film
• Side 2 Microprismatic Fluorescent Pink
• Figure shows Fluorescent Pink as Example

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Sign 4

• Yellow Microprismatic Landolt C on Purple
• Side 1 Background is Non-Reflective Purple Film,
  Legend is Microprismatic Normal Yellow
• Side 2 Background is Microprismatic Fluorescent
  Purple, Legend is Fluorescent Yellow
• Figure shows Fluorescent Purple as Example

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Sign 5

• Black Paint Pedestrian on Yellow Micro prismatic
• Side 1 Normal Yellow
• Side 2 Fluorescent Yellow Green
• Figure shows Fluorescent Yellow Green as Example

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Sign 6

• Black Paint PLANT ENTRANCE (Series C) on Yellow
  Microprismatic
• Side 1 Normal Yellow
• Side 2 Fluorescent Yellow
• Figure shows Normal Yellow as Example

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Test Site and Layout
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Test Site and Layout
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Results

• Calculation of the legibility distances
• subtracting travel distance from the overall
  start-to-sign distance for each sign
• Increase in legibility distance due to
  fluorescence is not very strong
• But still statistically significant

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Results Percent Increase in Legibility Distance
Due to Fluorescence
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Results

• Analysis of Variance (ANOVA)
• Landolt C Signs only
• Replication 1 3 data
• Effect of Fluorescence is small but statistically
  significant
• FFLUOR(1,26)17.778, p 0.003

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Sign 1 Black LC, Yellow or Fluorescent Yellow
Green Background
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Sign 2 Black LC, Yellow or Fluorescent Yellow
Background
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Sign 3 Black LC, Pink or Fluorescent Pink
Background
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Sign 4 Yellow/Fluorescent Yellow LC, Purple or
Fluorescent Purple Background
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Sign 5 Black Pedestrian Symbol, Yellow or
Fluorescent Yellow Green Background
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Sign 6 Black PLANT ENTRANCE, Yellow or
Fluorescent Yellow Background
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Discussion and Conclusion

• Adding the property of fluorescence to the colors
  used in this study did in fact statistically
  significantly increase the legibility distances
• However, increases were quite small from a
  practical point of view
• ranging from 5.3 to 15.9 when adding the
  property of fluorescence
• We hypothesize that the small increase in the
  legibility distance may be attributed to the
  increase in the color difference DEuv between
  the legend and the sign background and the
  increased background luminance, leading to an
  increased luminance contrast

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Discussion and Conclusion

• A word of caution
• Adding the property of fluorescence may
  potentially reduce legibility distance in some
  cases
• fluorescent positive contrast signs with
  non-fluorescent legend (not included in this
  study)
• For example white legend on fluorescent red
  background
• In such cases trade off the increased detection
  potential with a slight reduction in legibility
• In general, for negative contrast signs and for
  positive contrast signs where both the legend and
  the background are fluorescent, a slight increase
  in the legibility distance can be expected when
  adding the property of fluorescence