© 2015 Rensselaer Polytechnic Institute. All rights reserved. Luminous Intensity Requirements for Service Vehicle Warning Beacons (TRB Paper ) John D. Bullough, Mark S. Rea Lighting Research Center, Rensselaer Polytechnic Institute Transportation Research Board Annual Meeting January 11-15, 2015

© 2015 Rensselaer Polytechnic Institute. All rights reserved. Relevance of Warning Beacon Design to Safety  There are about 316,000 warning beacons in the U.S. (Cook et al. 2000; US Census 2009)  Workers in transportation, construction and utilities are over- represented in work-related fatalities (NIOSH 2014)  Improved beacon design could help prevent 70 fatalities and 5200 injuries annually in the U.S. (Cook et al. 2000) 2

© 2015 Rensselaer Polytechnic Institute. All rights reserved. Warning Beacon Performance Standards 3  Vehicle-mounted warning beacon performance is specified by several standards from the Society of Automotive Engineers (SAE) › SAE J595: Flashing Warning Lamps for Authorized Emergency, Maintenance and Service Vehicles Yellow: 1-2 flashes/second, peak intensity (when on) of 600 candelas Yellow: 1-2 flashes/second, peak intensity (when on) of 600 candelas › SAE J845: Optical Warning Devices for Authorized Emergency, Maintenance and Service Vehicles Yellow: 1-2 flashes/second, peak flash energy of 90 candela·seconds (emergencies), 22 candela·seconds (warning), 10 candela·seconds (identification) Yellow: 1-2 flashes/second, peak flash energy of 90 candela·seconds (emergencies), 22 candela·seconds (warning), 10 candela·seconds (identification) What is a candela·second?

© 2015 Rensselaer Polytechnic Institute. All rights reserved. Warning Beacon Performance Standards (cont’d.) 4  Warning beacon performance is specified by several standards from the Society of Automotive Engineers (SAE) › SAE J1318: Gaseous Discharge Warning Lamp for Authorized Emergency, Maintenance and Service Vehicles Yellow: 1-4 flashes/second, flash energy of candela·seconds (emergencies), 22 candela·seconds (warning), 10 candela·seconds (identification) Yellow: 1-4 flashes/second, flash energy of candela·seconds (emergencies), 22 candela·seconds (warning), 10 candela·seconds (identification)

© 2015 Rensselaer Polytechnic Institute. All rights reserved. Suitability of Existing Standards  The 600-cd luminous intensity value from SAE J595 is consistent with data from Howard and Finch (1960)  Intensity requirements do not take ambient conditions (e.g., daytime versus nighttime) into account › Presumably they are minima for daytime viewing › No maximum requirements for glare control 5

© 2015 Rensselaer Polytechnic Institute. All rights reserved. Experimental Method 6  Three laboratory experiments were conducted to measure response times to flashing warning beacons, and impacts on hazard visibility  Participants viewed a low-contrast target adjacent to or 5 o from a simulated truck with a warning beacon (LED: peak wavelength 590 nm, half-bandwidth 18 nm) with adjustable peak luminous intensity ( cd)

© 2015 Rensselaer Polytechnic Institute. All rights reserved. Experimental Conditions  Experiment 1: Simple scenes (day/night, on/off- axis location)  Experiment 2: Simple scenes with visual clutter (day/night, on/off-axis location)  Experiment 3: Realistic scenes (day/night, on/off- axis, with/without visual clutter)  Total n=17 (5F/12M), aged years (mean 49), with current driver’s licenses 7

© 2015 Rensselaer Polytechnic Institute. All rights reserved. 8 Simple Daytime Background Scene: Experiment 1

© 2015 Rensselaer Polytechnic Institute. All rights reserved. 9

Experiment 1 (No Clutter): Response Times 10 Response times to warning beacons viewed on-axis reached asymptotic (minimum) values for both daytime and nighttime conditions for the range of peak luminous intensities investigated. Response times to warning beacons viewed off-axis were asymptotic for nighttime conditions but not for daytime conditions. The interaction between ambient condition and peak luminous intensity on response times is evident.

© 2015 Rensselaer Polytechnic Institute. All rights reserved. Experiment 1 (No Clutter): Target Visibility Ratings 11 Ratings of fixation target visibility decreased slightly with higher on-axis warning beacon peak intensities for the nighttime conditions. Ratings of fixation target visibility were largely unaffected by off-axis warning beacons for all peak intensities.

© 2015 Rensselaer Polytechnic Institute. All rights reserved. 12

© 2015 Rensselaer Polytechnic Institute. All rights reserved. Experiment 2 (Visual Clutter): Response Times 13 Response times to warning beacons viewed on-axis reached asymptotic values for nighttime, but not daytime conditions for the range of peak luminous intensities. Response times to warning beacons viewed off-axis reached asymptotic values at higher peak intensities for daytime than for nighttime conditions.

© 2015 Rensselaer Polytechnic Institute. All rights reserved. Experiment 2 (Visual Clutter): Target Visibility Ratings 14 Ratings of fixation target visibility decreased slightly at the highest on-axis warning beacon peak intensity for nighttime conditions. Ratings of fixation target visibility were slightly lower under nighttime than daytime conditions at the highest off-axis warning beacons peak intensity.

© 2015 Rensselaer Polytechnic Institute. All rights reserved. 15 Realistic Daytime Background Scene, No Visual Clutter: Experiment 3

CAUTION 16

© 2015 Rensselaer Polytechnic Institute. All rights reserved. Experiment 3 (Realistic Scenes): Response Times 17 Response times to warning beacons viewed on-axis reached asymptotic values for the range of peak luminous intensities under both daytime and nighttime conditions. Response times to warning beacons viewed off-axis differed with and without clutter and between daytime and nighttime for the lowest peak intensity.

© 2015 Rensselaer Polytechnic Institute. All rights reserved. Experiment 3 (Realistic Scenes): Target Visibility Ratings 18 Ratings of fixation target visibility decreased very slightly at the highest on-axis warning beacon peak intensity for nighttime conditions. Ratings of fixation target visibility were largely unaffected by the off-axis warning beacon peak intensity.

© 2015 Rensselaer Polytechnic Institute. All rights reserved. Discussion  Luminous intensity specifications differing for daytime and nighttime are justified  SAE J595 luminous intensity requirements are reasonable for daytime viewing conditions but excessive for nighttime 19

© 2015 Rensselaer Polytechnic Institute. All rights reserved. Next Steps  Outdoor field trials will be conducted to validate laboratory study findings  Coordination of multiple warning beacons on one or more vehicles will also be investigated 20

© 2015 Rensselaer Polytechnic Institute. All rights reserved. A Roadway Incident Scene Today 21 Photo:

© 2015 Rensselaer Polytechnic Institute. All rights reserved. A Roadway Incident Scene Tomorrow? 22 Photo:

© 2015 Rensselaer Polytechnic Institute. All rights reserved. Acknowledgments  Sponsor: National Institute of Occupational Safety and Health (NIOSH Grant R01OH A1 to M. Rea)  Nicholas Skinner and Dennis Guyon, Lighting Research Center  Philip Garvey, Eric Donnell and Martin Pietrucha, Pennsylvania State University 23