Synthesis of the Advance in and Application of Fractal Characteristics of Traffic Flow
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Synthesis of the Advance in and Application of Fractal Characteristics of Traffic Flow Final Report Contract No. BDK80 977‐25 July 2013 Prepared by: Lehman Center for Transportation Research Florida International University Prepared for: Research Center Florida Department of Transportation Final Report Contract No. BDK80 977-25 Synthesis of the Advance in and Application of Fractal Characteristics of Traffic Flow Prepared by: Kirolos Haleem, Ph.D., P.E., Research Associate Priyanka Alluri, Ph.D., Research Associate Albert Gan, Ph.D., Professor Lehman Center for Transportation Research Department of Civil and Environmental Engineering Florida International University 10555 West Flagler Street, EC 3680 Miami, FL 33174 Phone: (305) 348-3116 Fax: (305) 348-2802 and Hongtai Li, Graduate Research Assistant Tao Li, Ph.D., Associate Professor School of Computer Science Florida International University 11200 SW 8th Street Miami, FL 33199 Phone: (305) 348-6036 Fax: (305) 348-3549 Prepared for: Research Center State of Florida Department of Transportation 605 Suwannee Street, M.S. 30 Tallahassee, FL 32399-0450 July 2013 DISCLAIMER The opinions, findings, and conclusions expressed in this publication are those of the authors and not necessarily those of the State of Florida Department of Transportation. iii METRIC CONVERSION CHART SYMBOL WHEN YOU KNOW MULTIPLY BY TO FIND SYMBOL LENGTH in inches 25.4 millimeters mm ft feet 0.305 meters m yd yards 0.914 meters m mi miles 1.61 kilometers km mm millimeters 0.039 inches in m meters 3.28 feet ft m meters 1.09 yards yd km kilometers 0.621 miles mi SYMBOL WHEN YOU KNOW MULTIPLY BY TO FIND SYMBOL AREA in2 square inches 645.2 square millimeters mm2 ft2 square feet 0.093 square meters m2 yd2 square yard 0.836 square meters m2 ac acres 0.405 hectares ha mi2 square miles 2.59 square kilometers km2 mm2 square millimeters 0.0016 square inches in2 m2 square meters 10.764 square feet ft2 m2 square meters 1.195 square yards yd2 ha hectares 2.47 acres ac km2 square kilometers 0.386 square miles mi2 SYMBOL WHEN YOU KNOW MULTIPLY BY TO FIND SYMBOL VOLUME fl oz fluid ounces 29.57 milliliters mL gal gallons 3.785 liters L ft3 cubic feet 0.028 cubic meters m3 yd3 cubic yards 0.765 cubic meters m3 mL milliliters 0.034 fluid ounces fl oz L liters 0.264 gallons gal m3 cubic meters 35.314 cubic feet ft3 m3 cubic meters 1.307 cubic yards yd3 NOTE: volumes greater than 1000 L shall be shown in m3 iv Technical Report Documentation Page 1. Report No. 2. Government Accession No. 3. Recipient's Catalog No. 4. Title and Subtitle 5. Report Date Synthesis of the Advance in and Application of Fractal Characteristics of July 2013 Traffic Flow 6. Performing Organization Code 7. Author(s) 8. Performing Organization Report No. Kirolos Haleem, Priyanka Alluri, Albert Gan, Hongtai Li, and Tao Li 9. Performing Organization Name and Address 10. Work Unit No. (TRAIS) Lehman Center for Transportation Research Florida International University 11. Contract or Grant No. 10555 West Flagler Street, EC 3680, Miami, FL 33174 BDK80 977-25 12. Sponsoring Agency Name and Address 13. Type of Report and Period Covered Research Center Final Report State of Florida Department of Transportation June 2012 – July 2013 605 Suwannee Street, M.S. 30, Tallahassee, Florida 32399-0450 14. Sponsoring Agency Code 99700-3596-119 15. Supplementary Notes Mr. Jacques Defrant, P.E., of the Florida Department of Transportation (FDOT) District 4 succeeded Mr. Felix Delgado, P.E., formerly also of FDOT District 4, as the Project Manager for this project. 16. Abstract Fractals are irregular geometric objects that exhibit finite details at all scales, and once magnified, their basic structures remain the same regardless of the scale of magnification. Fractal theory has been successfully applied in different fields of science. This project provides a synthesis of existing applications of fractal theory in various fields, as well as its potential applications in traffic management. The specific information gathered and summarized in this report includes: (1) a synthesis of fractal applications in fields that share similarities with transportation networks, such as electrical networks, and in fields outside of transportation; (2) a synthesis of fractal applications that have been proven effective in traffic flow; (3) additional insights on how fractal theory can be applied in traffic management strategies; and (4) summary of research findings and recommendations for more detailed research. Two fractal techniques, the fractal dimension and the Hurst exponent, were applied to detect the existence of fractal characteristics in traffic and crash data from Florida. Traffic volume, speed, and occupancy data obtained from 15- min and 1-hr detector data at two locations in Miami-Dade County were found to exhibit fractal characteristics. Furthermore, the speed trend revealed stronger fractal behavior compared to the volume and occupancy trends for the same time period. The existence of fractal characteristics in crash data was detected in both annual and daily frequency trends. However, the daily crash frequency trends exhibited greater extent of fractal behavior compared to the annual trends, mainly due to the existence of more random fluctuations. The fractal investigation of both annual and three-year average crash rates at ten randomly-selected signalized intersections revealed that the annual crash rate trend, in general, exhibited relatively more fractal characteristics than the three-year average trend. Future research could make use of the insights presented in this study to apply fractal theory in traffic management strategies such as managed lanes, ramp metering, crash analysis, and travel time reliability. Compared to traditional models, fractal theory is anticipated to yield more precise estimates of performance measures. Therefore, a potential future research is to apply fractal theory for predicting short-term traffic flow. Another promising avenue is to apply fractal theory to identify high-crash locations and to predict crash rate at specific locations. These approaches could potentially result in increased efficiency, mobility, and safety of the entire roadway network. 17. Key Word 18. Distribution Statement Fractal Theory, Fractal Characteristics, Traffic Flow, Traffic Prediction, Traffic Management, Traffic Safety 19. Security Classif. (of this report) 20. Security Classif. (of this page) 21. No. of Pages 22. Price Unclassified Unclassified 91 Form DOT F 1700.7 (8-72) Reproduction of completed page authorized v ACKNOWLEDGEMENTS This research was funded by the Research Center of the Florida Department of Transportation (FDOT) under the direction of Mr. Darryll Dockstader. We are particularly grateful to our Project Manager, Mr. Jacques Defrant, P.E., of the FDOT District 4, for his guidance and support throughout the project. We are also grateful to Mr. Felix Delgado, P.E., formerly also of the FDOT District 4, who preceded Mr. Defrant as the Project Manager. Last but certainly not the least, we would like to thank Ms. Vicki Morrison of the FDOT Research Center for her editing of this report. vi EXECUTIVE SUMMARY The main objective of this project is to provide a synthesis of existing applications of fractal theory in various fields, as well as potential applications of fractal theory in traffic management. The study also identifies those elements of traffic flow which exhibit fractal characteristics. The study further uses crash and traffic flow data from Florida to investigate the existence of fractal characteristics. The specific information gathered and summarized in this report includes: 1. A synthesis of fractal applications in fields that share similarities with transportation networks, such as electrical and water supply networks, and in fields outside of transportation, such as astronomy and ecology; 2. A synthesis of fractal applications that have been proven effective in traffic flow such as in traffic flow prediction; 3. Additional insights on how fractal theory can be applied to traffic management strategies, such as managed lanes, ramp metering, etc.; and 4. Summary of research findings and recommendations for more detailed research and development of future guidance documents. Fractals are irregular geometric objects that exhibit finite details at all scales, and when magnified, their basic structures remain the same regardless of the scale of magnification. The main characteristics of fractals are self-similarity, iterative process, infinite complexity, and existence of non-integer complex dimension. Common fractal analysis techniques are the Hurst exponent, the fractal dimension, the largest Lyapunov exponent, the power spectrum, and the Kolmogorov entropy. The main indicators of existence of fractal characteristics are as follows: the largest Lyapunov exponent should have a positive sign; the Hurst exponent (H) estimate should lie between 0 and 1; and the Kolmogorov entropy should have a positive sign. Moreover, larger estimates of the Lyapunov exponent, the Hurst exponent, and the fractal dimension indicate more complex fractal nonlinear characteristics. Fractal theory has been successfully applied in different fields of science, including but not limited to animal behavior studies, human health studies, economics, astronomy, ecology, physics, pavement engineering, environmental engineering, behavior of materials, and electrical networks. Even though application of fractal theory is not uncommon in several areas in transportation, such