Evaluation of 70 Mph Speed Limit in Kentucky Our Mission
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Research Report KTC-08-10/UI56-07-1F KENTUCKY TRANSPORTATION CENTER EVALUATION OF 70 MPH SPEED LIMIT IN 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. OUR VALUES 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. Research Report KTC-08-10/UI56-07-1F EVALUATION OF 70 MPH SPEED LIMIT IN KENTUCKY by Kenneth R. Agent Transportation Research Engineer 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 the report reflect the views of the author who is 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. The inclusion of manufacture names and trade names is for identification purposes and is not to be considered an endorsement. May 2008 1. Report No. 2. Government Accession No. 3. Recipient's Catalog No. KTC-08-10/UI56-07-1F 4. Title and Subtitle 5. Report Date May 2008 Evaluation of 70 MPH Speed Limit in Kentucky 6. Performing Organization Code 7. Author(s) 8. Performing Organization Report No.6 K. R. Agent KTC-08-10 9. Performing Organization Name and Address 10. Work Unit No. (TRAIS) Kentucky Transportation Center College of Engineering 11. Contract or Grant No. University of Kentucky Lexington, KY 40506-0281 13. Type of Report and Period Covered 12. Sponsoring Agency Name and Address Final Kentucky Transportation Cabinet State Office Building Frankfort, KY 40622 14. Sponsoring Agency Code 15. Supplementary Notes Study Title: Unforeseen Investigation 16. Abstract The objective of this study was to document the change in operating speeds of cars and trucks on rural interstates and parkways as a result of the change in speed limit from 65 mph to 70 mph. The 85th percentile speed increased 1.3 mph for cars (74.6 to 75.9 mph) and 0.6 mph for trucks (69.8 to 70.4 mph) on rural interstates and 2.0 mph for cars (73.5 to 75.5 mph) and 1.2 mph for trucks (69.5 to 70.7 mph) on four-lane parkways. The increase in speed limits on a limited number of roads did not result in an increase in speeds on other highway types. There is a large difference between the 85th percentile speed and posted speed limit on non-interstate and parkway roads which were designed to accommodate higher speeds. 17. Key Words 18. Distribution Statement speed limit 85th percentile speed Unlimited, with approval of the Kentucky Transportation Cabinet 19. Security Classif. (of this report) 20. Security Classif. (of this page) 21. No. of Pages 22. Price Unclassified Unclassified 15 TABLE OF CONTENTS Page Executive Summary............................................................ i 1.0 Background ............................................................1 2.0 Procedure..............................................................2 3.0 Results................................................................3 4.0 Conclusions............................................................5 5.0 Recommendations .......................................................5 6.0 References.............................................................6 Tables ......................................................................7 Appendix....................................................................9 EXECUTIVE SUMMARY The Kentucky legislature enacted a law in 2007 which identified specific roads (rural interstates and rural, four-lane parkways) where the speed limit could be raised to 70 mph from 65 mph. The speed limit applies to all vehicles with no difference between cars and trucks. The objective of this study was to document the change in operating speeds of cars and trucks on rural interstates and parkways as a result of the change in speed limit. Speeds on other types of roads were also obtained. The evaluation consisted of a comparison of operating speeds of cars and trucks on various types of roads before and after implementation of the 70 mph speed limit. All of the data were collected using a moving radar procedure where speeds of opposing vehicles were obtained while driving down the highway. Data were collected for vehicles not affected by other vehicles or roadway character. The before data were obtained in April through June 2007 with the after data taken from September 2007 through April 2008. Vehicles were classified as either a car or truck. As a comparison to speed data collected on rural interstates and parkways, data were also collected on urban interstates, two lane parkways, a few two lane roads with full width shoulders, and some non-interstate or parkway four lane roads with full width shoulders. The increase in speed limits on rural interstates and four-lane parkways from 65 to 70 mph only resulted in a small increase in travel speeds. The 85th percentile speed increased 1.3 mph for cars and 0.6 mph for trucks on rural interstates and 2.0 for cars and 1.2 mph for trucks on four-lane parkways. Speeds for trucks are less than for cars with a difference of about five mph on rural interstates and four-lane parkways. The increase in speed limits on a limited number of roads did not result in an increase in speeds on other highway types. There is a large difference between the 85th percentile speed and posted speed limit on non-interstate and parkway roads which were designed to accommodate higher speeds. The data support retention of the 70 mph speed limit on rural interstates and rural, four- lane parkways. The large difference in the 85th percentile speed and posted speed limit on a few other road types justify an increase in speed limit for a limited number of high-design type roads. For example, an increase in the speed limit from 55 to 60 mph on two-lane parkways and other roads designed to accommodate higher speeds would be appropriate. The difference in operating speeds of cars and trucks shows that a different speed limit for cars and trucks may be considered in some instances. If a different speed limit was used, data show the speed limit would be five mph higher for cars than for trucks. i 1.0 BACKGROUND Recent legislation in Kentucky allowed the speed limit on rural interstates and parkways to be increased to 70 mph from 65 mph (1). The specific roads where the Secretary of Transportation could increase the speed limit to 70 mph were listed in the legislation. The speed limit on these roads had been 65 mph for many years. A previous evaluation of speed limits in Kentucky examined criteria and procedures used for setting speed limits and recommended maximum speed limits for various types of roads (2). The recommendation was made that the 85th percentile speed should be used as the standard method to establish speed limits since this speed reflects operating speeds as determined by the overall roadway environment. The Manual on Uniform Traffic Control Devices (MUTCD) (3) states that the posted speed limit should be within five mph of the 85th percentile speed of free- flowing traffic. The MUTCD allows two types of speed limit signs; one to designate passenger car speeds (including any nighttime information or minimum speed) and the other to show special speed limits for trucks and other vehicles. The previous study (completed in 1997) found that travel speeds for most types of highways were substantially above the posted speed limit (2). Also, speeds of cars were slightly above those of trucks. For rural interstates, the 85th percentile speed was 72.9 percent for cars and 68.7 percent for trucks with 70 percent of cars and 37 percent of trucks traveling at a speed over the 65 mph speed limit. For rural parkways, the 85th percentile speed was 73.6 mph for cars and 69.7 mph for trucks with the speed of 71 percent of cars and 45 percent of trucks over the 65 mph speed limit. The recommended speed limits for rural interstates and parkways were 70 mph for cars and 65 mph for trucks (2). Since the 1997 study, the speed limit on rural interstates in many states has increased to 70 mph while Kentucky’s speed limit on this type of road remained at 65 mph. A 2007 summary of speed limits across the United States on various types of roads showed that 19 states had a speed limit of 70 mph on rural interstates with 13 states having a speed limit of 75 mph on these roads (4). In 11 states the speed limit for trucks is less than cars on rural interstates. Also, for roads other than interstates and other limited access roads, 22 states had a speed limit for cars of over 55 mph. As previously noted, the Kentucky legislature enacted a law in 2007 which identified specific roads (rural interstates and rural, four-lane parkways) where the speed limit could be raised to 70 mph. The speed limit was raised on all the allowed roads in July 2007. The speed limit applies to all vehicles with no difference between cars and trucks. The objective of this study was to document the change in operating speeds of cars and trucks on rural interstates and parkways as a result of the increase in speed limit from 65 to 70 mph. Speeds on other types of roads were also obtained. 1 2.0 PROCEDURE The evaluation consisted of a comparison of operating speeds of cars and trucks on various types of roads before and after implementation of the 70 mph speed limit on rural interstates and rural, four-lane parkways.