Evaluation of Speed Limits in Kentucky (KYSPR 96-172)
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Research Report KTC-97-06/SPR96-172 KENTUCKY TRANSPORTATION CENTER College of Engineering EVALUATION OF SPEED LIMITS IN KENTUCKY UNIVERSITY OF KENTUCKY Our 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. We Value... Teamwork -- Listening and Communicating, Along with Courtesy and Respect for Others Honesty and Ethical Behavior Delivering the Highest Quality Products and Services Continuous Improvement in All That We Do For more information or a complete publication list, contact us at: KENTUCKY TRANSPORTATION CENTER 176 Raymond Building University of Kentucky Lexington, Kentucky 40506-0281 (859) 257-4513 (859) 257-1815 (FAX) 1-800-432-0719 www.engr.uky.edu/ktc [email protected] The University of Kentucky is an Equal Opportunity Organization Research Report KTC-97-6 EVALUATION OF SPEED LIMITS IN KENTUCKY (KYSPR-96-172) by Kenneth R. Agent Research Engineer Jerry G. Pigman Research Engineer and Joel M. Weber Research Assistant Kentucky Transportation Center College of Engineering University of Kentucky Lexington, Kentucky in cooperation with Kentucky Transportation Cabinet Commonwealth of Kentucky and Federal Highway Administration U.S. Department of Transportation 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 Cabinet, or the Federal Highway Administration. This report does not constitute a standard, specification, or regulation. April 1997 TABLE OF CONTENTS Page List of Tables .......................................................................................................................... ii Executive Summary ................................................................................................................ iii 1.0 Introduction ...................................................................................................................1 2.0 Procedure ......................................................................................................................2 2.1 Review of Literature ........................................................................................3 2.2 Speed Data .........................................................................................................3 2.2.1 Moving Speeds.........................................................................................3 2.2.2 Speed Monitoring Stations.......................................................................4 2.2.3 Speed Limit Changes ...............................................................................4 2.2.4 Construction Zone Speeds .......................................................................5 2.3 Accident Data.....................................................................................................5 2.3.1 Characteristics of Speed-Related Accidents ............................................5 2.3.2 Speed Limit Changes ...............................................................................5 2.3.3 65 mph versus 55 mph Interstate Speed Limits.......................................6 3.0 Results ............................................................................................................................6 3.1 Review of Literature ..........................................................................................6 3.1.1 Methods Used to Establish Speed Limits ................................................6 3.1.2 Results of Changing Speed Limits...........................................................7 3.1.3 Differential Speed Limits.........................................................................8 3.1.4 Current Status of Speed Limits................................................................8 3.2 Speed Data .........................................................................................................9 3.2.1 Moving Speeds on Various Highway Types ...........................................9 3.2.2 Speed Monitoring Data by Type of Highway........................................10 3.2.3 Speed Data Before and After Speed Limit Change ...............................11 3.2.4 Construction Zone Speeds .....................................................................13 3.3 Accident Data...................................................................................................13 3.3.1 Characteristics of Speed-Related Accidents ..........................................13 3.3.2 Locations with High Number of Speed Related Accidents ...................15 3.3.3 Accident Data Before and After Speed Limit Change...........................16 3.3.4 Accident Rates for 65 mph versus 55 mph Interstates...........................17 4.0 Conclusions..................................................................................................................18 4.1 Speed Data .......................................................................................................18 4.2 Accident Data...................................................................................................18 5.0 Recommendations........................................................................................................19 5.1 Establish Speed Limits.....................................................................................19 5.2 Speed Limits ....................................................................................................19 Appendix A Review of Literature.........................................................................................49 Appendix B Moving Speed Data for Specific Highways .....................................................69 Appendix C Speed Monitoring Data for Specific Locations................................................77 Appendix D Locations with High Number of Speed-Related Accidents 83 i LIST OF TABLES Table 1. Moving Speed Data for Various Highway Types (Cars) Table 2. Moving Speed Data for Various Highway Types (Trucks) Table 3. Example Comparisons of Speed Limit versus Operating Speed (Cars) Table 4. Speed Monitoring Data by Type of Highway (1994 and 1995) Table 5. Speeds Before and After Speed Limit Change Table 6. Speed Data in Construction Zones (Cars) Table 7. Speed Data in Construction Zones (Trucks) Table 8. Characteristics of Speed-Related Accidents (1993-1995) Table 9. Characteristics of Fatal Speed-Related Accidents (1993-1995) Table 10. Percent of Speed-Related Accidents by County (1993-1995) Table 11. Speed-Related Accidents by Highway Type (1992-1994) Table 12. Accidents Before and After Speed Limit Change Table 13. Comparison of Accident Data for Adjacent Sections of Interstates with 65 mph and 55 mph Speed Limits Table 14. Recommended Maximum Speed Limits Table B-1. Moving Speed Data for Specific Highways (Cars) Table B-1. Moving Speed Data for Specific Highways (Trucks) Table C-1. Speed Monitoring Station Data for Specific Locations (1994 and 1995) Table D-1. One-Mile Sections with Highest Critical Rate Factor for Speed- Related Accidents (1992-1994 Accidents) ii EXECUTIVE SUMMARY The objectives of this study were to examine current criteria and procedures used for setting speed limits on public roads and to recommend appropriate maximum speed limits for various types of roads. The study involved three major areas. These were: review of literature, collection and analysis of speed data, and collection and analysis of accident data. The speed data included collecting data on various highway types using the “moving” radar mode, use of data from speed monitoring stations, comparison of spot speed data before and after speed limit changes, and both moving and spot speed data at construction zones. Accident data were collected at locations where speed limits were changed and also on sections of adjacent interstates with different speed limits. A recommendation is that the 85th percentile speed should be used as the standard method to establish speed limits. The speed limit should be posted in 5 mph increments and should be obtained by rounding the 85th percentile speed down to the nearest speed value in miles per hour that end in 5 or 0. The posted speed limit may be set at a speed where the minimum design speed for an entire road may allow the design speed for a specific location to be less than the speed limit. In those instances, advisory speed signs may be used to warn drivers to reduce their speed to less than the posted speed limit. An exception to the use of the 85th percentile speed would be for legislatively mandated speed limits. The speed data show that a large percentage of vehicle speeds exceed currently posted speed limits. The highest percentage exceeding the limit was on urban interstates and two-lane parkways where the speed limit was 55 mph. The speeds for trucks were slightly less that for cars on all types of highways with a difference of less than 5 mph when the 85th percentile speed is considered. A comparison of speed data at locations where speed limits were changed showed differences but not dramatic changes. The data support the theory that drivers will drive what they consider an appropriate speed regardless of the speed limit. A comparison of accident rates at adjacent sections of interstate where the speed limit was 55 and 65 mph did not find