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Cover images: Federal Highway Administration 2 Technical Report Documentation Page 1. Report No. 2. Government Accession 3. Recipient’s Catalog No. FHWA-HOP-17-003 No. 4. Title and Subtitle 5. Report Date Synthesis of Variable Speed Limit Signs May 2017 6. Performing Organizations Code 7. Authors 8. Performing Organization Bryan Katz, Jiaqi Ma, Heather Rigdon, Kayla Sykes, Report No. Zhitong Huang, Kelli Raboy 9. Performing Organization Name and Address 10. Work Unit No. (TRAIS) Leidos 11251 Roger Bacon Drive 11. Contract or Grant No. Reston, VA 20190 Contract No. DTFH61-12-D-00045 ToXcel, LLC Task T-5009 7140 Heritage Village Plaza Gainesville, VA 20155 12. Sponsoring Agency Name and Address 13. Type of Report and Period U.S. Department of Transportation Covered Federal Highway Administration Research Synthesis, 1200 New Jersey Avenue, SE March 2016–December 2016 Washington, DC 20590 14. Sponsoring Agency Code HOTM 15. Supplementary Notes Jimmy Chu, HOTM, Government Task Manager (GTM) 16. Abstract Variable speed limit (VSL) systems utilize information on traffic speed, occupancy, and volume detection, weather, and road surface conditions to determine the appropriate speeds at which drivers should be traveling, given current roadway and traffic conditions.The use of VSL during less than ideal conditions, such as heavy traffic and adverse weather, can improve safety by decreasing the risks associated with traveling at speeds that are higher than appropriate for the conditions and by reducing speed variance in traffic. In addition, VSL can be used to dynamically manage speeds during planned (rush hour congestion) and unplanned (incidents) events. Used in conjunction with managed lanes and other active traffic management strategies, VSL can respond to downstream congestion to eliminate or delay bottlenecks and mitigate the possibility of crashes. Based on a comprehensive literature review along with agency interviews to gather information on existing, deactivated and planned VSL systems, this synthesis provides a comprehensive review of current practices on VSL operations, particularly experiences from deployments in the United States, and to identify successful and best practices from the following perspectives: planning and policy, design, deployment, and standards, operations and maintenance, and outcomes. 17. Key Words 18. Distribution Statement Variable speed limit; planning and policy; design; deployment; No restrictions. standards; operations and maintenance; active traffic management 19. Security Classif. (of this report) 20. Security Classif. (of this 21. No of Pages 22. Price Unclassified page) Unclassified 100 N/A Form DOT F 1700.7 (8-72) Reproduction of completed page authorized. SYNTHESIS OF VARIABLE SPEED LIMIT SIGNS SI* (MODERN METRIC) CONVERSION FACTORS APPROXIMATE CONVERSIONS TO SI UNITS 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 AREA in.2 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 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 NOTE: volumes greater than 1,000 L shall be shown in m3 MASS oz ounces 28.35 grams g lb pounds 0.454 kilograms kg T short tons (2000 lb) 0.907 megagrams Mg (or "t") (or "metric ton") TEMPERATURE (exact degrees) °F Fahrenheit 5 (F-32)/9 or Celsius °C (F-32)/1.8 ILLUMINATION fc foot-candles 10.76 lux lx fl foot-Lamberts 3.426 candela/m2 cd/m2 FORCE and PRESSURE or STRESS lbf poundforce 4.45 newtons N lbf/in.2 poundforce 6.89 kilopascals kPa per square inch *SI is the symbol for the International System of Units. Appropriate rounding should be made to comply with Section 4 of ASTM E380. (Revised March 2003). iii SYNTHESIS OF VARIABLE SPEED LIMIT SIGNS SI* (MODERN METRIC) CONVERSION FACTORS (CONTINUED) APPROXIMATE CONVERSIONS TO SI UNITS SYMBOL WHEN YOU KNOW MULTIPLY BY TO FIND SYMBOL LENGTH mm millimeters 0.039 inches in. m meters 3.28 feet ft m meters 1.09 yards yd km kilometers 0.621 miles mi AREA mm2 square millimeters 0.0016 square inches in.2 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 VOLUME 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 MASS g grams 0.035 ounces oz kg kilograms 2.202 pounds lb Mg (or "t") megagrams 1.103 short tons (2000 lb) T (or "metric ton") TEMPERATURE (exact degrees) °C Celsius 1.8C+32 Fahrenheit °F ILLUMINATION lx lux 0.0929 foot-candles fc cd/m2 candela/m2 0.2919 foot-lamberts fl FORCE and PRESSURE or STRESS N newtons 0.225 poundforce lbf kPa kilopascals 0.145 poundforce lbf/in2 per square inch *SI is the symbol for the International System of Units. Appropriate rounding should be made to comply with Section 4 of ASTM E380. (Revised March 2003). iv SYNTHESIS OF VARIABLE SPEED LIMIT SIGNS Table of Contents EXECUTIVE SUMMARY .................................................................................................................. 1 PURPOSE OF REPORT ......................................................................................................................1 METHODOLOGY ...............................................................................................................................1 KEY RESULTS ......................................................................................................................................2 CHAPTER 1. INTRODUCTION ........................................................................................................ 3 SHORT DESCRIPTION .......................................................................................................................3 HISTORY AND PREVIOUS RESEARCH ............................................................................................4 CHAPTER 2. RESEARCH METHODOLOGY .................................................................................... 5 LITERATURE REVIEW ........................................................................................................................5 AGENCY OUTREACH ........................................................................................................................5 SYNTHESIS AND ANALYSIS .............................................................................................................7 CHAPTER 3. VARIABLE SPEED LIMIT STATE OF THE PRACTICE ................................................. 9 REPRESENTATIVE VARIABLE SPEED LIMIT SYSTEMS IN THE UNITED STATES ......................9 VARIABLE SPEED LIMIT SYSTEMS USED FOR CONGESTION-BASED ACTIVE TRAFFIC MANAGEMENT ................................................................................................................................10 VARIABLE SPEED LIMIT SYSTEMS USED FOR WORK ZONES ..................................................12 VARIABLE SPEED LIMIT SYSTEMS USED FOR WEATHER .........................................................12 DEACTIVATED VARIABLE SPEED LIMIT SYSTEMS IN THE UNITED STATES ..........................13 LESSONS LEARNED ........................................................................................................................14 CHAPTER 4. FINDINGS ................................................................................................................ 17 PLANNING AND POLICY ................................................................................................................17 DESIGN, DEPLOYMENT AND STANDARDS ................................................................................21 OPERATIONS AND MAINTENANCE .............................................................................................24 OUTCOMES ......................................................................................................................................32 v SYNTHESIS OF VARIABLE SPEED LIMIT SIGNS Table of Contents (Continued) CHAPTER 5. CONCLUSION – BENEFITS AND CHALLENGES OF VARIABLE SPEED LIMIT SYSTEMS ................................................................................................................ 39 KEY BENEFITS ..................................................................................................................................39 KEY CHALLENGES