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Driver Awareness of Highway Sites with High Skid Accident Potential 6 TE Report No. FHWA-RD- 74-66 oo2 #i /^w-^L_ no . DRIVER AWARENESS OF HIGHWAY SITES FHWA- RD- WITH HIGH SKID ACCIDENT POTENTIAL 74-66 Dept. Of Tr c, ^ w » ! — F. R. Hanscom Library •^KS O* July 1974 Final Report This document is available to the public through the National Technical Information Service, Springfield, Virginia 22161 Prepared for FEDERAL HIGHWAY ADMINISTRATION Offices of Research & Development Washington, D.C. 20590 DISCLAIMER NOTICE This document is disseminated under the sponsorship of the Department of Transportation in the interest of information exchange. The United States Government assumes no liability for its contents or use thereof. The contents of this report reflect the view of the author, who is responsible for the facts and the accuracy of the data presented herein. The contents do not necessarily reflect the official views or policy of the Department of Transportation. This report does not constitute a standard, specification, or regulation. FHWA DISTRIBUTION NOTICE Sufficient copies of this report are being distributed by FHWA Bulletin to provide at least one copy to each region and division office, and two copies to each State highway agency. Direct distribution is being made to •the division offices. TECHNICAL REPORT STANDARD TITLE PAGE 1. Report No. 1. Government Accession No. 3. Recipient's Catalog No. FHWA-RD- 74-66* £ 4. Title and Subtitle 5. Report Date July 1974 ^ Driver Awareness of Highway Sites With High Skid Accident Potential 6. Performing Organization Code 7. Author(s) 8. Performing Organization Report No. fbept Of Is :ation Fred R. Hanscom SKID Final 9. Performing Organization Name and Address 10. Work Unit No. " t1 f\R i BioTechnology, Inc. FCP 31H6012 3027 Rosemary Lane 11. Contract or Grant No. DOT-FH-11-7972 Falls Church, Virginia 22042 library 13. Type of Report and Period Covered and Addres* 12. Sponsoring Agency Name Final Report (January 1973 - Traffic Systems Division, Office of Research July 1974) \\ Federal Highway Administration. 14. Sponsoring Agency Code Washington, D.C. 20590 15. Supplementary Notes Contract Manager for this study: Alfred G. Klipple, HRS-31. This volume contains the research report with Appendices A and B. Appendix C, Computer Printout of Questionnaire Analysis, is a separate, limited distribution document. 16. Abstract This field study examined driver responses to two types of potential highway skidding hazard: wet pavements subjected to high frictional driving demands, and bridges during periods of possible preferential icing. Study objectives were to examine motorists' general awareness of the hazards and to assess the relative effectiveness of various signing treatments which warn of the hazards. Measures of signing effectiveness were motorists' speeds at critical driving locations and questionnaire responses regarding motorists' observations and interpretations of the signs. Three curved highway sections were treated with five experimental signing conditions. Variations on the "Slippery When Wet" symbolic sign ranged from its use by itself, through increasing levels of specificity and conspicuity, to its use with flashing lights and an advisory speed limit. Experimental signing conditions incorporating flashing lights were effective at reducing highest quartile mean speeds below the critical safe wet pavement speed based on roadway geometry and surface conditions. Questionnaire results indicated that 60 percent of the interviewed motorists saw and properly interpreted the more conspicuous warning signs. Motorists' cues of potential hazard were observed to be: roadway curvature and superelevation, behavior of other motorists, appearance of pavement surface, ambient conditions, known site accident history, and presence of the warning sign. About one percent of the interviewed motorists cited the warning sign as their cue of potential skidding hazard. Two bridge approaches were signed using combinations of activated and nonactivated signs both at the bridge and in advance of the bridge during periods of possible preferential icing. Significant speed reductions on the bridge and at the bridge entry point were elicited by activated signing. Activated signing used at the bridge was observed to have a greater impact than activated signing used at the advance location. Drivers were more responsive to the signs during periods when the hazard was greater. 17. Key Words 18. Distribution Statement Skidding Hazard, Warning Signs, Skid Warning Signs, No restrictions. This document is available to the public Driver Characteristics, Icy Bridge Warning Signs, through the National Te chnical Information Service, Traffic Studies Springfield, Virginia 22151. 19. Security Clossif. (of this report) 20. Security Clossif. (of this page) 21. No. of Pages 22. Price Unclassified Unclassified 216 Form DOT F 1700.7 (8-69) ACKNOWLEDGMENTS The conduct of this study was dependent upon the efforts of numerous individuals asso- ciated with diverse; organizations. The cooperation and contributions of the following indi- viduals are most gratefully acknowledged. Federal Highway Administration, Office of Research Alfred G. Klipplc, Contract Manager Michael D. Freilas John Richer Richard Schwab Federal Highway Administration, Office of Traffic Operations James McDonald Federal Highway Administration, Office of Development John R. Watson, Jr. Maryland State Highway Administration Lee Billingsley M. Sladc Caltrider Thomas Hicks Robert Keel F. Stanley Kinney Maryland State Police Sgt. Arnold, Rockville Lt. Carey, Greenbelt Lt. Tucker, Hagerstown Many State Troopers Virginia Department of Highways John P. Mills, Jr. Virginia State Police Captain W.R. Wagner Sgt. J.C. Ogburd Fairfax, Virginia City Police Inspector Lenard Kline Penn State University Thomas Gillespie W.E. Meyer Richard Olsen University of Pittsburgh John M. Roberts Judith Fine Allen Weather Corporation Louie Allen Charles Miller llx BioTechnology, Inc. Program Management Harold Price Data Collection Tom Brown Allen Shinder Margaret Forsythe Traffic Evaluator System Application Christopher Nerone Editorial Inputs Sally Craig Data Analysis Inputs James Sanders Wallace Berger Chang Yoo Part-time Support Brian Portmann Denise Schaffer MT/SC Report Preparation and Graphics Janet Jones Lynn Caldwell IV ABSTRACT This field study examined driver responses to two types of potential highway skidding hazard: wet pavements subjected to high frictional driving demands, and bridges during periods of possible preferential icing. Study objectives were to examine motorists' general awareness of the hazards and to assess the relative effectiveness of various signing treatments which warn of the hazards. Measures of signing effectiveness were motorists' speeds at critical driving locations and questionnaire responses regarding motorists' observations and interpretations of the signs. Three curved highway sections were treated with five experimental signing conditions. Variations on the "Slippery When Wet" symbolic sign ranged from its use by itself, through increasing levels of specificity and conspicuity, to its use with flashing lights and an advisory speed limit. Experimental signing conditions incorporating flashing lights were effective at reducing highest quartile mean speeds below the critical safe wet pavement speed based on roadway geometry and surface conditions. Signing without flashing lights was not shown to be effective. Questionnaire results indicated that 60 percent of the interviewed motorists saw and properly interpreted the more conspicuous warning signs. Motorists' cues of potential hazard were observed to be: roadway curvature and superelevation, behavior of other motorists, appearance of pavement surface, ambient conditions, known site accident history, and presence of the warning sign. About one percent of the interviewed motorists cited the warning sign as their cue of potential skidding hazard. Two bridge approaches were signed using combinations of activated and nonactivated signs both at the bridge and 1,000 feet in advance of the bridge during periods of possible preferential icing. Significant speed reductions on the bridge and at the bridge entry point were elicited by activated signing. The most effective sign condition was advance and bridge located activated signing used during hours of darkness. Activated signing used at the bridge was observed to have a greater impact than activated signing used at the advance location. Drivers were more responsive to the signs during periods when the hazard was greater. Bridge approach roadway geometry was seen to impact on motorists' observation and speed reduction in response to the signing. Improved results were obtained on the short sight-distance approach where the bridge did not visually compete for driver attention. V TABLE OF CONTENTS Page Introduction 1 Literature Review 3 Skid Resistance-Factors and Measurement 3 The Driver and Skid Potential 11 Traffic Signing Considerations 18 Bridge Icing 29 Warning Signs and Skidding Liability 38 Skid Hazard Liability 38 Selected Case Studies .45 Study Procedures . 48 Experimental Design . 48 Skid Resistance Measurement . 52 Development of Signing Concepts .54 Identification and Characterization of Sites .57 Data Collection Procedures 68 Analysis and Results 77 Traffic Evaluator System Data (Wet Pavement Conditions) .77 General Warning Sign Effects .77 Site 1 78 Site 2 95 Site 3 .101 Overview of Sign Evaluation 103 Special Study: Effects of Increased Conspicuity 107 Ministudies: Driver Responses to Rainfall Onset . .109
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