Evaluation of the Impact of Spectral Power Distribution on Driver Performance PUBLICATION NO. FHWA-HRT-15-047 AUGUST 2015 Research, Development, and Technology Turner-Fairbank Highway Research Center 6300 Georgetown Pike McLean, VA 22101-2296 FOREWORD The Federal Highway Administration’s Office of Safety Research and Development focuses on conducting research that promotes a safe driving environment while offering practical considerations to address the needs of practitioners. Roadway lighting offers significant safety benefits but also represents a substantial share of the operating budgets of agencies tasked with maintaining the lighting infrastructure. Therefore, there is a need to optimize the safety implications and budgetary considerations. This report provides the details and results of a comprehensive investigation of the impact of light-source spectrum on driver visual performance. In a series of human factors experiments, the effect of overhead lighting and headlamp spectral power distribution was evaluated with respect to driver detection and recognition of large and small objects. The report also discusses the spectral interaction of headlamp and roadway lighting on the detection of pedestrians, including an evaluation of enhanced pedestrian detection through a momentary peripheral illumination mechanism of the vehicle headlamps. Monique R. Evans Director, Office of Safety Research and Development Notice This document is disseminated under the sponsorship of the U.S. Department of Transportation in the interest of information exchange. The U.S. Government assumes no liability for the use of the information contained in this document. This report does not constitute a standard, specification, or regulation. The U.S. Government does not endorse products or manufacturers. Trademarks or manufacturers’ names appear in this report only because they are considered essential to the objective of the document. Quality Assurance Statement The Federal Highway Administration (FHWA) provides high-quality information to serve Government, industry, and the public in a manner that promotes public understanding. Standards and policies are used to ensure and maximize the quality, objectivity, utility, and integrity of its information. FHWA periodically reviews quality issues and adjusts its programs and processes to ensure continuous quality improvement. TECHNICAL REPORT DOCUMENTATION PAGE 1. Report No. 2. Government Accession 3. Recipient’s Catalog No. FHWA-HRT-15-047 No. 4. Title and Subtitle 5. Report Date Evaluation of the Impact of Spectral Power August 2015 Distribution on Driver Performance 6. Performing Organization Code: 7. Author(s) 8. Performing Organization Report No. Ronald B. Gibbons, Jason Meyer, Travis Terry, Rajaram Bhagavathula, Alan Lewis, Michael Flanagan, Caroline Connell 9. Performing Organization Name and Address 10. Work Unit No. Virginia Tech Transportation Institute 11. Contract or Grant No. 3500 Transportation Research Plaza (0536) DTFH61-10-C-00032 Blacksburg, VA 24061 12. Sponsoring Agency Name and Address 13. Type of Report and Period Covered Office of Safety Research and Development 09/24/2010–01/31/2015 Federal Highway Administration 14. Sponsoring Agency Code 6300 Georgetown Pike McLean, VA 22101-2296 15. Supplementary Notes The Contracting Officer’s Representatives were Clayton Chen and Abdul Zineddin, Office of Safety Research and Development. 16. Abstract This project is a complete investigation of the impact of light-source spectrum on driver visual performance. In a series of human factors experiments, the effect of overhead lighting and headlamp spectral power distribution was evaluated with respect to driver detection and recognition of large and small objects and pedestrians. The potential for applying mesopic multiplying factors to roadway lighting was also evaluated, as was a momentary peripheral illuminator system’s effects on driver visual performance and eye-glance behavior. The results indicate that, although the momentary peripheral illuminator improved one measure of pedestrian detection, it was also a distraction to drivers. The results also indicate that at higher speeds, neither light-source spectrum nor mesopic multiplying factors apply, but mesopic multiplying factors are applicable to lighting design for lower-speed roadways and other nondriving environments. 17. Key Words 18. Distribution Statement Light sources, Spectral effects roadway No restrictions. This document is available through lighting, Roadway safety, Lighting the National Technical Information Service; levels, Lighting and safety Springfield, VA 22161. http://www.ntis.gov/about/contact.aspx 19. Security Classif. (of this report) 20. Security Classif. (of this page) 21. No. of 22. Unclassified Unclassified Pages Price 236 Form DOT F 1700.7 (8-72) Reproduction of completed page authorized ii TABLE OF CONTENTS EXECUTIVE SUMMARY .......................................................................................................... 1 CHAPTER 1. INTRODUCTION ................................................................................................ 5 PROJECT OBJECTIVES ....................................................................................................... 5 CHAPTER 2. BACKGROUND ................................................................................................... 7 IMPACT OF ROADWAY LIGHTING ................................................................................. 7 Color ..................................................................................................................................... 10 MESOPIC EFFECTS AT NIGHT FOR DRIVERS ........................................................... 11 Models of Mesopic Vision .................................................................................................... 13 LIGHTING AND THE DRIVING ENVIRONMENT ........................................................ 17 Visual Acuity ........................................................................................................................ 17 Age Effects on Vision and Driving ....................................................................................... 18 Visibility and Contrast .......................................................................................................... 18 Size (Visual Angle) ............................................................................................................... 20 Contrast Polarity Factor ........................................................................................................ 21 Exposure Time ...................................................................................................................... 21 Age Factor ............................................................................................................................. 21 Transient Adaptation ............................................................................................................. 22 Eccentricity ........................................................................................................................... 22 MOMENTARY PERIPHERAL ILLUMINATORS ........................................................... 22 Problems Detecting Pedestrians at Night .............................................................................. 23 Headlamp Technologies ........................................................................................................ 24 SPECIFICATION DEVELOPMENT FOR AN MPI SYSTEM ........................................ 27 Conceptual Design of an MPI System .................................................................................. 27 Pedestrian-Detection Systems ............................................................................................... 28 CHAPTER 3. EXPERIMENTAL APPROACH ...................................................................... 31 MATERIALS AND FACILITIES ........................................................................................ 32 Virginia Smart Road ............................................................................................................. 32 Overhead-Lighting Systems .................................................................................................. 33 Vehicles and Headlamp Systems .......................................................................................... 35 Visual Objects ....................................................................................................................... 37 DEPENDENT VARIABLES ................................................................................................. 40 Detection Distance ................................................................................................................ 40 Color-Recognition Distance .................................................................................................. 41 Orientation-Recognition Distance ........................................................................................ 42 PROCEDURES ....................................................................................................................... 42 Participant Selection ............................................................................................................. 42 Participant Screening ............................................................................................................ 43 Experimental Runs ...............................................................................................................