PHYSIOLOGICAL PARAMETERS INFLUENCING TRAFFIC SIGN DESIGN

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CHAPTER 2. LITERATURE REVIEW

The primary literature review for this research focused on studies involving fluorescent materials, but also included pertinent aspects of the driving population and traffic control devices. While research with fluorescent signing material has been conducted in the past, there have not been any on-road studies investigating the conspicuity of fluorescent signs. Previous research by Barker (1998) addresses the importance of conspicuity as it relates to the use of non-fluorescent signs and incident management trailblazing. Additional research (Dewar, 1988, 1989, 1993; Mace, 1988;U.S. Department of Transportation, 1983) describes necessary evaluation and design criteria for traffic signs, so these aspects will not be discussed herein. Physiological Parameters Influencing Traffic Sign Design Most equipment and systems are designed to be operated by a broad spectrum of people. In designing equipment for adjustability, it is typically the practice to provide for adjustments to cover the range from the 5th percentile female to the 95th percentile male(Sanders and McCormick, 1993). Alternatively, the worst-case scenario of drivers’ needs must be factored into the design of traffic signs (Dewar, 1989). Consideration must be given to reduced visual acuity of older drivers (as well as visually impaired younger drivers), individuals with slow reaction times, and individuals with a greater than normal susceptibility to confusion due to information overload. Information contained in the Traffic Control Devices Handbook (U.S. Department of Transportation, 1983) addresses factors that must be considered in the overall design of traffic signs. These factors are important considerations that ultimately allow motorists to safely and effectively traverse the roadways. Use of fluorescent signing material has the potential to lessen the impact of adverse physiological effects brought on by the aging process

Conspicuity

Conspicuity refers to “the property of an object that causes it to attract attention or to be readily located by search” (Cole and Hughes, 1984). Factors that influence conspicuity of a sign are characteristics of the sign and the environment in which it is used. Important sign-related variables that determine daytime conspicuity are the size of the sign, its contrast with the immediate surroundings, and the complexity of the background (Jenkins and Cole, 1986). Van Norren (1981) cited sign placement location, driver expectations, and frequency of occurrence of the sign as factors contributing to conspicuity. In addition, sign color and fluorescent materials exhibit the potential for improving conspicuity (Burns and Johnson, 1997; Zwahlen and Schnell, 1997).According to Engel (1976), conspicuity can be viewed as being either sensory or cognitive in nature. Sensory conspicuity can be categorized as the degree of visual prominence afforded a sign by its crude sensory features (brightness, color, size,legibility) that combine to ensure that its message content is available at the preattentive level of processing. The cognitive conspicuity of a sign is based on its meaning, novelty, or relevance and will depend to a great extent on the psychological state of the driver, his purpose, and his expectations at the time (Jenkins and Cole, 1986). Conspicuity, in the visual (sensory) context, can be defined as the attribute of an object that ensures its presence is noticed at the preattentive level of processing (Jenkins and Cole, 1986). It is essential that priorities be allocated to the enormous amount of information available in today’s road environment. This is important so that the driver can direct his attention to only those items that are necessary for his purpose and safety. What information the driver considers important, and thus pays attention to, depends on the message of the sign and its relevance to him at the time. Therefore, some degree of preattentive processing of all available traffic environment information must occur so that the important information is not discarded but progresses to the stage of consciously being used. Information conveyed to drivers by traffic signs must be visually prominent,legible, and comprehensible at the preattentive level of processing. If not, it will not warrant attention and its importance cannot be evaluated.
Research by Zwahlen and Schnell (1997) tentatively concluded that to maximize daytime conspicuity for peripheral detection and recognition, highly conspicuous fluorescent colors (such as fluorescent yellow-green) along with a fairly large target size should be selected. Earlier research by Zwahlen and Vel (1994) concluded “designers of traffic signs, personal conspicuity enhancement items and devices, and roadside traffic control devices should consider the superior visual conspicuity properties of fluorescent colors (especially fluorescent yellow and fluorescent orange) and incorporate them in designs when the highest possible daytime target conspicuity is absolutely necessary.” “Strong yellow-green” (SYG)1 is one of the unassigned colors listed in the Federal Highway Administration’s (FHWA’s) “Manual on Uniform Traffic Control Devices” (Department of Transportation, 1988). Fluorescent yellow-green (FYG) is very promising since it is more conspicuous in low-light conditions than conventional yellow signing materials. The visible spectrum for color is between 370 – 730 nm. Peak wavelength sensitivity (scotopic, 507 nm; photopic, 555 nm) supports the outstanding visibility aspects of FYG (Cornsweet, 1970). The FHWA has sponsored numerous studies involving the evaluation of FYG signs that warn drivers of non-motorized hazards (Blakely, Clark, Dutt, and Hummer, 1996; Clark, Hummer, and Dutt, 1996; Dhar and Woodin, 1995; Dutt, Hummer, and Clark, 1997)

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DEDICATION
ACKNOWLEDGMENTS 
LIST OF FIGURES
LIST OF TABLES
CHAPTER 1. INTRODUCTION
CHAPTER 2. LITERATURE REVIEW
PHYSIOLOGICAL PARAMETERS INFLUENCING TRAFFIC SIGN DESIGN
CONSPICUITY
AGE RELATED FACTORS
DAYTIME VERSUS NIGHTTIME DRIVING FACTORS
WORK ZONE APPLICATIONS AND CONSIDERATIONS
OTHER FLUORESCENT MATERIAL APPLICATIONS
SUMMARY 
CHAPTER 3. RESEARCH OBJECTIVES
EXPERIMENTAL HYPOTHESES
CHAPTER 4. METHODS AND MATERIALS
EXPERIMENTAL DESIGN 
INDEPENDENT VARIABLES
CONTROLLED VARIABLES
DEPENDENT VARIABLES
PARTICIPANTS 
APPARATUS 
Titmus® II Vision Tester
Automobile
Experimental Sign Design
Post-test Questionnaire
PROCEDURE
CHAPTER 5. RESULTS & DISCUSSION
DRIVING PERFORMANCE VARIABLES 
Late Braking Maneuvers
ANALYSIS OF WRONG AND MISSED TURNS 
Assessment for Sign Color
Assessment for Age 
Assessment for Visibility Condition 
DRIVER PREFERENCE DATA 
Survey Question #1: How Visible was the Test Detour Sign Relative to the Environment?
Survey Question #2: How Easy was it to Identify, or Understand, the Directional Information
Provided by the Test Signs?
Survey Question #3: How Useful Would You Find this Type of Sign Design for Providing Temporary
Directional/Detour Information While Driving?
Survey Question #4: Rank the Sample Signs in Order of Preference for Visibility Along the Roadway, by
Sign Color.
Survey Question #5: Rank the Sample Signs in Order of Preference Based on How Easy You Feel the Signs are to Read.
Survey Question #6: Rank the Sample Signs in Order of Overall Preference for Use on Signs Providing Temporary Directional/Detour Information.
CHAPTER 6: CONCLUSIONS, RECOMMENDATIONS, AND
FUTURE RESEARCH DIRECTIONS
CONCLUSIONS 
RECOMMENDATIONS 
LIMITATIONS OF THIS RESEARCH AND DIRECTIONS OF FUTURE RESEARCH 
REFERENCES
APPENDICES
APPENDIX A. PARTICIPANT INFORMATION
APPENDIX B: MAP OF TEST ROUTE AREA
APPENDIX C: DESCRIPTION OF THE INSTRUMENTED VEHICLE
Forward-View Camera
Multiplexer and PC-VCR
Data Collection Computer
Sensors
Experimenter Control Panel and Event Flagger
Video/Sensor/Experimenter Control Panel Interface
Safety Apparatus
APPENDIX D: APPARATUS AND PROCEDURES FOR LAB MEASUREMENTS AND RESULTS OF FIELD MEASUREMENTS
APPENDIX E: POST-TEST QUESTIONNAIRE
APPENDIX F: INITIAL CONTACT AND SCREENING FORMS
APPENDIX G: INFORMED CONSENT FORM
APPENDIX H. VISION AND COLOR TEST SCRIPTS
APPENDIX I. SCRIPTS OF TEST INSTRUCTIONS AND PROCEDURES
APPENDIX J: STATISTICAL TABLES FOR SURVEY QUESTIONS
VITA

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