JOINT TRANSPORTATION RESEARCH PROGRAM INDIANA DEPARTMENT OF TRANSPORTATION AND PURDUE UNIVERSITY Identifying Effects and Applications of Fixed and Variable Speed Limits Michelle M. Mekker, Stephen M. Remias, Margaret L. McNamara, Wayne A. Bunnell, Drake W. Krohn, James R. Sturdevant, Edward D. Cox, Darcy M. Bullock SPR-3900 • Report Number: FHWA/IN/JTRP-2016/31 • DOI: 10.5703/1288284316358 RECOMMENDED CITATION Mekker, M. M., Remias, S. M., McNamara, M. L., Bunnell, W. A., Krohn, D. W., Sturdevant, J. R., Cox, E. D., & Bullock, D. M. (2016). Identifying effects and applications of fixed and variable speed limits (Joint Transportation Research Program Publication No. FHWA/IN/JTRP-2016/31). West Lafayette, IN: Purdue University. https://doi.org /10.5703 /1288284316358 AUTHORS Michelle M. Mekker Graduate Research Assistant Lyles School of Civil Engineering James R. Sturdevant, PE Purdue University Indiana Department of Transportation Stephen M. Remias, PhD Director, Traffic Management Division Assistant Professor of Civil Edward D. Cox, PE and Environmental Engineering Director, ITS Engineering College of Engineering Indiana Department of Transportation Wayne State University Darcy M. Bullock, PhD, PE Margaret L. McNamara Professor of Civil Engineering Wayne A. Bunnell Lyles School of Civil Engineering Drake W. Krohn Purdue University Graduate Research Assistants (765) 494-2226 Lyles School of Civil Engineering [email protected] Purdue University Corresponding Author JOINT TRANSPORTATION RESEARCH PROGRAM The Joint Transportation Research Program serves as a vehicle for INDOT collaboration with higher education institutions and industry in Indiana to facilitate innovation that results in continuous improvement in the planning, https://engineering.purdue.edu/JTRP/index_html design, construction, operation, management and economic efficiency of the Indiana transportation infrastructure. Published reports of the Joint Transportation Research Program are available at http://docs.lib.purdue.edu/jtrp/. NOTICE DepartmentThe contents of of Transportation this report reflect or the the Federal views of Highway the authors, Administration. who are responsible The report for does the not facts constitute and the accuracya standard, of the data presented herein. The contents do not necessarily reflect the official views and policies of the Indiana specification, or regulation. COPYRIGHT Copyright 2016 by Purdue University. All rights reserved. Print ISBN: 978-1-62260-457-9 ePUB ISBN: 978-1-62260-458-6 TECHNICAL REPORT STANDARD TITLE PAGE 1. Report No. 2. Government Accession No. 3. Recipient's Catalog No. FHWA/IN/JTRP-2016/31 4. Title and Subtitle 5. Report Date August 2016 Identifying Effects and Applications of Fixed and Variable Speed Limits 6. Performing Organization Code 7. Author(s) 8. Performing Organization Report No. Michelle M. Mekker, Stephen M. Remias, Margaret L. McNamara, Wayne A. Bunnell, Drake W. Krohn, Edward D. Cox, James R. Sturdevant, Darcy M. Bullock FHWA/IN/JTRP-2016/31 9. Performing Organization Name and Address 10. Work Unit No. Joint Transportation Research Program Purdue University 11. Contract or Grant No. 550 Stadium Mall Drive SPR-3900 West Lafayette, IN 47907-2051 12. Sponsoring Agency Name and Address 13. Type of Report and Period Covered Indiana Department of Transportation Final Report State Office Building 100 North Senate Avenue 14. Sponsoring Agency Code Indianapolis, IN 46204 15. Supplementary Notes Prepared in cooperation with the Indiana Department of Transportation and Federal Highway Administration. 16. Abstract In Indiana, distracted driving and unexpected queues have led to an increase in the amount of back-of-queue crashes, particularly on approach to work zones. This report presents new strategies for the assessment of both transportation safety and traffic operations using crowd-sourced probe vehicle data and a speed laser vehicle re-identification scheme. This report concludes by recommending strategies for the placement of variable speed limits (VSL) adjacent to work zones and suggestions for future research. 17. Key Words 18. Distribution Statement speed limits, variable speed limits, mobility No restrictions. This document is available to the public through the National Technical Information Service, Springfield, VA 22161. 19. Security Classif. (of this report) 20. Security Classif. (of this page) 21. No. of Pages 22. Price Unclassified Unclassified 69 Form DOT F 1700.7 (8-69) EXECUTIVE SUMMARY Lastly, portable variable speed limit signs were deployed adjacent to a work zone in southern Indiana and an empirical IDENTIFYING EFFECTS AND APPLICATIONS analysis was done to develop best practices. This report presents a OF FIXED AND VARIABLE SPEED LIMITS new methodology to evaluate the impact of variable speed limit signage based on individual vehicle-matching. The speeds and speed changes of these matched vehicles were used to analyze Introduction individual driver response to the variable speed limits. The new vehicle-matching methodology showed that after observing a In Indiana, distracted driving and unexpected queues have led 15 MPH speed drop on a single variable speed limit sign for cars to an increase in the amount of back-of-queue crashes, particu- (10 MPH for trucks) over three separate variable speed limit larly on approach to work zones. This report presents new stra- signs, cars reduced their speed by a median of 3.3 MPH (2.1 MPH tegies for the assessment of both transportation safety and traffic for trucks). Overall, 3.5% of cars and 11.1% of trucks complied operations using crowdsourced probe vehicle data and a speed with the 55 MPH speed limit after observing three variable speed laser vehicle re-identification scheme. This report concludes by limit signs. Using a similar assessment strategy, variable speed recommending strategies for the placement of variable speed limit signs were deployed in pairs and evaluated. Sign pairs limits (VSL) adjacent to work zones and suggestions for future consist of two portable variable speed limit signs in one loca- research. tion, one on each side of the roadway. When assessing a similar The first portion of this study characterizes the back-of-queue 15 MPH speed drop (10 MPH for trucks) it was discovered that concerns using a new assessment technique based on crash reduc- three sets of paired signs are more effective in slowing down tion factors. Crash reduction factors are widely used by engineers vehicles, with reductions of 4.7 MPH for passenger vehicles and 2.7 MPH for trucks relative to three individual signs. Compliance for prioritizing safety investments. Work zones are routinely anal- rates after the three sign locations were 3.3 and 9.1 for cars yzed by the length and duration of queues. Queue detection warn- % % and trucks, respectively. ing technology has been growing in availability and reliability in recent years. Three years of crash data and crowdsourced probe vehicle data were analyzed to classify crashes as being associated Findings with queueing conditions or free-flow conditions. In 2014, only 1.2% of the distanced-weighted hours of operation of Indiana The final recommendations gathered for this study include: interstates operated at or under 45 MPH. A three-year study on Indiana interstates indicates that commercial vehicles were N Paired variable speed limit signs outperform single signs involved in 87% of back-of-queue fatal crashes compared to 39% when attempting to slow vehicles. of all fatal crashes during free-flow conditions. A new mea- N Operators and managers should use at least three pairs of sure of crash rate was developed to account for the presence and variable speed limit signs to obtain any tangible reduction in duration of queues: crashes per mile-hour of congestion. The con- driver speeds. gested crash rate on all Indiana interstates in 2014 was found to N Variable speed limit signage should be placed upstream of be 24 times greater than the uncongested crash rate. Queues were the expected back-of-queue location. found to be present for five minutes or longer prior to approxi- N Placement of variable speed limit signage can be actively mately 90% of congestion crashes in 2014. This information monitored using crowdsourced probe vehicle data. shows the importance of developing technology that can warn N Future work should be considered including automating the motorists of traffic queues. speed limits on the variable speed limit signage. CONTENTS INTRODUCTION ................................................................ 1 1.BACKGROUND............................................................... 1 1.1Back-of-QueueCrashes(Motivation)............................................... 1 1.2StaticSpeedLimits............................................................ 2 1.3VariableSpeedLimits.......................................................... 3 2.DATASOURCES.............................................................. 3 2.1 Spot Speed vs. Space Mean Speed Data ............................................. 3 2.2ProbeVehicleData........................................................... 3 2.3CrashDatabase.............................................................. 4 2.4SpeedLaserMeasurements...................................................... 7 3. STUDY 1: LONGITUDINAL INTERSTATE CRASH SUMMARY (MOTIVATION) ............ 9 3.1 Fatal Crashes............................................................... 10 3.2 Classifying Interstate Crashes in 2014.............................................. 11 3.3