Abstract Findley, Daniel Jonathan
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ABSTRACT FINDLEY, DANIEL JONATHAN. A Comprehensive Two-Lane, Rural Road Horizontal Curve Study Procedure. (Under the direction of Joseph E. Hummer and William Rasdorf.) Horizontal curves are relatively dangerous features, with collision rates typically three times that of comparable tangent sections on average. To help make these segments safer, this research developed a comprehensive study procedure for rural, two-lane horizontal curves. To provide the basis for a comprehensive procedure, this research includes an examination of curve crash characteristics, an investigation of study methods for geometric characteristics, and recommendations for potential countermeasures. A complete and accurate data set on a horizontal curve is important for a transportation agency to make a well-informed decision on possible improvements that could enhance the safety of the roadway. However, many agencies do not know curve radii or lengths because drawings do not exist and inventories are not available. Typically, the analysis of a horizontal curve or set of curves for safety purposes by a highway agency is based on field visits and the judgment of experienced personnel. Many agencies rely on a drive-through by an engineer or technician and a small set of countermeasures that have proven themselves through the years. Analytical tools for curves have existed for a number of years; however, such tools have not been widely implemented due to the large number of competing highway safety objectives, real or perceived difficulties in collecting the necessary data, and calibrating models for local conditions, among other reasons. The publication of the Highway Safety Manual (HSM) offers the chance to overcome this impasse and get agencies to use crash models routinely. The HSM contains a crash prediction model for horizontal curves and estimates of crash modification factors (CMFs) for the most popular curve countermeasures. The model and CMFs have been approved by a committee of leading safety researchers and practitioners, which provides credibility to the tools. Application of the HSM is expected to be an appropriate methodology to identify curves with higher than normal crash potential, to be used to complement collision-based methods for curve safety analysis. This research developed a CMF to account for the effect of nearby curves on safety that can supplement HSM procedures. Several contributions to the practice of transportation engineering have resulted from this research. This research presents a new horizontal curve study method procedure to ensure a systematic approach for identifying curves, studying and measuring their characteristics, and improving hazardous locations. This research quantifies the collision characteristics of horizontal curves and created a linking of common horizontal curve collision types and effective countermeasures, which provides an engineer with the necessary information to identify and correct hazardous curves. This research recommends study methods for geometric characteristics which allows an engineer to most effectively and efficiently measure, define, and analyze horizontal curves to determine their predicted safety performance. The focus of these study methods is office procedures for collecting horizontal curve data, which are generally more efficient than field methods. This research establishes a set of parameters to which safety can be related through spatial and geometrical features. Safety was related geometrically through the establishment of guidance for horizontal curves for the implementation of the nationally accepted prediction model for roadways, presented in the Highway Safety Manual. Safety was related spatially through the impact of spatial relationships on horizontal curve safety using the predictive methodology of the Highway Safety Manual as a foundation for incorporating spatial considerations into horizontal curve safety prediction. The comprehensive curve study method procedure includes: horizontal curve identification, investigation and inventory, analysis, evaluation, and a recommendation of appropriate countermeasures. A systematic approach for identifying, investigating, analyzing, and evaluating horizontal curves can lead to the selection and evaluation of promising curves, and a recommendation of appropriate countermeasures. © Copyright 2011 by Daniel Jonathan Findley All Rights Reserved A Comprehensive Two-Lane, Rural Road Horizontal Curve Study Procedure by Daniel Jonathan Findley A dissertation submitted to the Graduate Faculty of North Carolina State University in partial fulfillment of the requirements for the Degree of Doctor of Philosophy Civil Engineering Raleigh, North Carolina 2011 APPROVED BY: ________________________________ ________________________________ Dr. Joseph Hummer, Co-Chair Dr. William Rasdorf, Co-Chair ________________________________ ________________________________ Dr. Nagui Rouphail Dr. Hugh Devine DEDICATION This dissertation is dedicated to my family and the educators I have had the privilege of learning from throughout my life. My entire family has supported me in all of my academic aspirations, for which I am eternally grateful. To my wife, Rachel, who provided unwavering support throughout my graduate education and the initial encouragement to start this endeavor. To my daughter, Sophia, who provided inspiration and an often needed diversion from my studies. To my parents, Frank and Jan, who provided immeasurable experiences and guidance that instilled a passion for learning and exploration. To my grandmothers, Jane and Barbara, whose kindness and praise always encouraged me and my grandfathers, whose academic and professional accomplishments have inspired me. To my sisters, Amy and Julie, who willingly supported my engineering curiosity with countless toys to reverse engineer. ii BIOGRAPHY Mr. Daniel J. Findley has a broad range of transportation experiences and skills. He is currently a Senior Research Associate at the Institute for Transportation Research and Education (ITRE) who has played a major role in the several projects relating to many fields of transportation including: pedestrian, highway, ferry, aviation, and bicycle. Mr. Findley also possesses a Professional Engineer’s (PE) license in the state of North Carolina. Mr. Findley is the son of Frank and Jan Findley. He was raised in Robbinsville, NC and graduated as the valedictorian of Robbinsville High School in 2001. After high school, he attended North Carolina State University and graduated Summa Cum Laude with a Bachelor of Science in Civil Engineering degree in 2005 and a Master of Science in Civil Engineering degree in 2006. iii ACKNOWLEDGEMENTS I would like to acknowledge the help and support of numerous individuals who assisted in the completion of my research. Dr. Joseph Hummer and Dr. William Rasdorf served as co- chairs for my committee and were instrumental in supporting and guiding my research efforts. The experience through this research in the realm of highway design and highway safety have been immense and allowed for my growth as a transportation professional. Dr. Nagui Rouphail and Dr. Hugh Devine were committee members and also provided meaningful feedback on my research. I appreciate the time and effort each of my committee members have demonstrated. I’m truly grateful for my experience as a student at NC State, where I have the opportunity to work closely with some of the top transportation researchers in the United States. I would also like to express my sincere gratitude for the opportunity to work with and learn from Charles Zegeer at the UNC Highway Safety Research Center. I am appreciative for the support I have had at the Institute of Transportation Research and Education (ITRE) from my colleagues and supervisors. My supervisor, Robert Foyle, has provided me with valuable experience which was important for my growth as an engineer and researcher. I would also like to thank Christopher Cunningham and Dr. Bastian Schroeder for their collaboration on many research projects which has enabled me to gain much appreciated experience. I would also like to thank the North Carolina Department of Transportation who funded the research project that formed this basis of this dissertation work. I had the privilege to work with many individuals at the North Carolina Department of Transportation who provided excellent support and direction, including: Brian Mayhew, Brian Murphy, and Shawn Troy with the Traffic Safety Systems Section; Jay Bennett and the Roadway Design Unit; Jennifer Brandenburg and the State Road Management Unit; and Charlie Brown and Betsy Pope of the Locations and Surveys Unit. iv TABLE OF CONTENTS List of Tables ........................................................................................................................... xi List of Figures ........................................................................................................................ xiii 1.0 Introduction .............................................................................................................. 1 1.1 Step 1: Site Identification ......................................................................................... 2 1.2 Step 2: Office Data Acquisition ............................................................................... 3 1.3 Step 3: Collision Data Analysis ............................................................................... 3 1.4 Step 4: Curve Characteristics Analysis ...................................................................