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Development of an Improved Method for Determining Advisory Speeds on Horizontal Curves KENTUCKY TRANSPORTATION CENTER 176 Raymond Building, University of Kentucky 859. 257. 4513 www.ktc.uky.edu Development of an Improved Method for Determining Advisory Speeds on Horizontal Curves Kentucky Transportation Center Research Report — KTC-16-14/SPR15-507-1F DOI: https://doi.org/10.13023/KTC.RR.2016.14 KTC’s Mission We provide services to the transportation community through research, technology transfer, and education. We create and participate in partnerships to promote safe and effective transportation systems. © 2017 University of Kentucky, Kentucky Transportation Center Information may not be used, reproduced, or republished without KTC’s written consent. Kentucky Transportation Center 176 Oliver H. Raymond Building Lexington, KY 40506-0281 (859) 257-4513 www.ktc.uky.edu Research Report KTC-16-14/SPR15-507-1F Development of an Improved Method for Determining Advisory Speeds on Horizontal Curves Eric. R. Green, P.E. Research Engineer Kenneth Agent, P.E. Research Engineer and Erin Lammers Research Engineer Kentucky Transportation Center College of Engineering University of Kentucky Lexington, Kentucky In Cooperation With Kentucky Transportation Cabinet Commonwealth of Kentucky The contents of this report reflect the views of the authors, who are responsible for the facts and accuracy of the data presented herein. The contents do not necessarily reflect the official views or policies of the University of Kentucky, the Kentucky Transportation Center, the Kentucky Transportation Cabinet, the United States Department of Transportation, or the Federal Highway Administration. This report does not constitute a standard, specification, or regulation. The inclusion of manufacturer names or trade names is for identification purposes and should not be considered an endorsement. July 2016 1. Report No. 2. Government Accession No. 3. Recipient’s Catalog No KTC-16-14/SPR15-507-1F 4. Title and Subtitle 5. Report Date Development of an Improved Method for Determining Advisory Speeds July 2016 on Horizontal Curves 6. Performing Organization Code 7. Author(s): 8. Performing Organization Report No. Eric R. Green, Kenneth Agent, Erin Lammers KTC-16-14/SPR15-507-1F 9. Performing Organization Name and Address 10. Work Unit No. (TRAIS) Kentucky Transportation Center College of Engineering University of Kentucky 11. Contract or Grant No. Lexington, KY 40506-0281 SPR 15-507 12. Sponsoring Agency Name and Address 13. Type of Report and Period Covered Kentucky Transportation Cabinet State Office Building 14. Sponsoring Agency Code Frankfort, KY 40622 15. Supplementary Notes Prepared in cooperation with the Kentucky Transportation Cabinet 16. Abstract Horizontal curves are an integral part of the highway alignment. However, a disproportionately high number of severe crashes occur on them. One method transportation agencies use to reduce the number crashes at horizontal curves is the installation of curve warning signs which post an appropriate advisory speed. Appropriate curve advisory speeds can be determined using several methods. Some of these methods are time-consuming to perform and are error-prone. The purpose of this research was to find the most efficient and accurate data collection method for determining curve advisory speeds. Several processes were developed and tested. They were then validated against the results of a manual process referred to as the Direct Method and other traditional methods (such as the ball-bank indicator), which are generally assumed to produce accurate results. Comparing the results of these methods lets researchers evaluate their accuracy and usefulness for setting advisory speeds. The results illustrate the potential of a more user-friendly methodology that allows for efficient and accurate data collection. The advisory speeds determined by this research will assist the Kentucky Transportation Cabinet to properly sign horizontal curves. Previous research suggests that posting appropriate advisory speeds results in a safer driving experience. 17. Key Words 18. Distribution Statement curve advisory speed, CARS, Rieker, superelevation, curve radius, TRAMS Unlimited with approval of the ball-bank indicator Kentucky Transportation Cabinet 19. Security Classification (report) 20. Security Classification (this page) 21. No. of Pages 19. Security Unclassified Unclassified 37 Classification (report) Table of Contents Executive Summary ....................................................................................................................................... 3 1. Introduction and Background ............................................................................................................... 3 2. Available Methods ................................................................................................................................ 4 2.1 Direct Method ............................................................................................................................... 4 2.2 Digital Ball-Bank Indicator ............................................................................................................. 4 2.3 Curve Advisory Reporting Service (CARS) ..................................................................................... 5 2.4 TRAMS ........................................................................................................................................... 6 2.5 Highway Information System ........................................................................................................ 7 2.6 Arc Method ................................................................................................................................... 7 3 Methodology ......................................................................................................................................... 8 3.1 Data collection .............................................................................................................................. 8 3.1.1 Direct Method Collection Process ......................................................................................... 9 3.1.2 Digital Ball-Bank Indicator (DBBI) Collection Process ........................................................... 9 3.1.3 CARS Collection Process ...................................................................................................... 11 3.1.4 TRAMS ................................................................................................................................. 13 3.1.5 Highway Information Systems ............................................................................................ 14 3.1.6 Arc Method ......................................................................................................................... 14 3.2 Reconciliation of Various Methods ............................................................................................. 15 4 Results and Conclusions ...................................................................................................................... 16 5 Conclusions and Recommendations ................................................................................................... 23 6 References .......................................................................................................................................... 24 2 Executive Summary Horizontal curves are an integral part of the highway alignment. However, a disproportionately high number of severe crashes occur on them (1). One method transportation agencies use to reduce the number of crashes at horizontal curves is the installation of curve warning signs which post an appropriate advisory speed. Appropriate curve advisory speeds can be determined using several methods. Some of these methods are time-consuming to perform and are error-prone. The purpose of this research was to find the most efficient and accurate data collection method for determining curve advisory speeds. Cost effectiveness was also taken into consideration when evaluating each method’s value. Several processes were developed and tested. They were then validated against the results of a manual process referred to as the Direct Method and other traditional methods (such as the ball-bank indicator), which are generally assumed to produce accurate results. Comparing the results of these methods allow researchers evaluate their accuracy and usefulness for setting advisory speeds. The results illustrate the potential of a more user-friendly methodology that allows for efficient and accurate data collection. The advisory speeds determined by this research will assist the Kentucky Transportation Cabinet properly sign horizontal curves, which previous research suggests results in a safer driving experience. 1. Introduction and Background In the United States, severe crashes occur in disproportionate numbers on horizontal curves. Each year, approximately 33,000 fatalities result from crashes, with 25 percent of these taking place on horizontal curves. (3) Approximately 85 percent of the fatal crashes that occur on horizontal curves involve roadway departures due in part to vehicles moving at excessively high speeds. (12) Warning signs posted near curves alert drivers to approaching changes in road geometry, but they do not establish an enforceable speed limit for curves. Advisory speed plaques are used to encourage speed reductions. (3) Curve warning signs and advisory speed plaques are classified as advance warning signs, and are mounted on the same
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