value metrics: quantifying lighting benefits for roadways · 2021. 2. 16. · 2018 cie ds 026...
TRANSCRIPT
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Value Metrics: Quantifying Lighting Benefits for Roadways
Rajaram Bhagavathula, PhD
Center for Infrastructure-Based Safety Systems
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Effects of (or lack of) Roadway Lighting
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What metrics can be used to quantify roadway lighting?
• Crashes
• Light Distribution
• Color or Spectral Power Distribution
• Light Level
Standards and Specifications have lagged with advent of LED roadway lighting
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Roadway Lighting and Traffic Safety –Decrease in Crash Metrics On Interstates
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ghte
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Gibbons, Ronald B., et al. Guidelines for the Implementation of Reduced Lighting on Roadways. No. FHWA-HRT-14-050. United States. Federal Highway Administration, 2014.
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Roadway Lighting & Safety –Decrease in Crashes at Intersections
Li, Y. E., Bhagavathula, R., Terry, T. N., Gibbons, R. B., & Medina, A. (2020). Safety Benefits and Best Practices for Intersection Lighting(No. FHWA/VTRC 20-R31).
Increase in light level by 1 Lux is associated with decrease in Night to Day Crash Ratio by 2.9 %
235 intersections in Virginia
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Lighting Variable
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Exponential Function
Rec Min =1.8 lx Rec Min =1.5 lx
Rec Min =2.6 lx Rec Min =1.6 lx
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Problems with using Crash Data
• Crashes are rare and extreme scenarios - 37000 traffic fatalities per 3.2 trillion miles travelled (2018)• 1 death per 86 million miles
• 1 injury per 1.3 million miles
• 1 crash per 508,000 miles
• Crashes are not a good metric to evaluate lighting• Multiple causal factors
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Crash Trifecta
Existing Unsafe
Condition
Driver Behavior
Unexpected Event
Crash
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We cannot light our way to seeing better or feeling safer!
No increase beyond 2 lux
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Visibility
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Bhagavathula, R., & Gibbons, R. B. (2020). Light levels for parking facilities based on empirical evaluation of visual performance and user perceptions. Leukos, 16(2), 115-136.
84% reduction in energy by dimming to 2 lux
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What areas should be illuminated by street lights?
Anchorage. Photo by Wayne Johnson, ML&P
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High vs. Low Surround Ratio
High Surround Low Surround
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How does Surround Ratio affect Visual Performance
Speed
Offset Distance from Roadway
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Future Directions to Evaluate Roadway Lighting
• Study probability distributions of detection in different light conditions• “How does the probability of detecting a hazard change with distance travelled?”
• Compare Detection distance to Stopping Sight Distance (SSD)• Easy for traffic engineers
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Effect of Light Level on Probability Distribution
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Comparison to Stopping Sight Distance
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Detection Distance (m)
SSD = 78.3 m
Percentile of Drivers Detected at SSD
Light LevelPercentile of Drivers Detectedat Distance Greater Than SSD
No Lighting 0
8 lux 73
12 lux 86
16 lux 88
21 lux 91
Can be used to identify how many drivers could have detected the hazard from a safe distance
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Comparison of lighting to other countermeasures
Advancing Transportation Through Innovation 15
• Best combination to increase pedestrian safety at night – In progress
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Driver visual performance under different light sources – Evidence of benefits of 4000 K LED
Advancing Transportation Through Innovation
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National Academies of Sciences, Engineering, and Medicine 2020. Solid-StateRoadway Lighting Design Guide: Volume 2: Research Overview. Washington, DC:The National Academies Press. https://doi.org/10.17226/25679.
Clanton, N., Gibbons, R., Garcia, J., & Terry, T. (2014). Evaluation of Adaptive Lighting in the City of Seattle.
Replace a 4000 K with a 3000 K• What is the increase in light level to match performance?• Side effects of the increase
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Use 3000 K CCT
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Roadway Light’s Effect on Soybean Growth
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Effect of Roadway Light Level on Yield and R-Stage of Soybeans
Palmer, M., Gibbons, R., Bhagavathula, R., & Holshouser, D. (2018). Roadway Lighting’s Impact on Altering Soybean Growth–Volume 2: LED versus HPS Color Spectral Impact. Illinois Center for Transportation/Illinois Department of Transportation.
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Does Roadway Lighting affect Facility Use or Physical Activity?
Advancing Transportation Through Innovation
Increase in Average Illuminance by 1 lux → Increase in Night to Day Pedestrian Count Ratio by 11.8%
Inform the lighting design and guidelines for pedestrian walkways and bicycle lanes.
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Roadway lighting and human health
• Lack of research on LED street lighting’s effect on human sleep physiology and alertness• Light with a higher blue content (LEDs)
• Affects sleep physiology by melatonin suppression
• Contrastingly, also increases alertness (some evidence)
• Studies in naturalistic roadway lighting exposures are in progress – almost done
• How much light do we get from street lights vs. other light exposures?• Indoor Light
• Electronic Devices
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Roadway Lighting 2 hour exposure - Drivers
Light Condition Road Luminance (cd/m2) Total Dose (lux-s)Avg. Corneal Illuminance per second (lux)
2200 K LED 0.8 9,448.00 1.3
3000 K LED 1 12,518.90 1.7
4000 K LED 1 12,663.00 1.8
5000 K LED 1 12,745.10 1.8
2100 K HPS 1 11,397.90 1.6
No Light <0.05 6,150.00 0.9
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Photometric Measures with Calculated α-opic Lux Values2018 CIE DS 026 Standard, CIE User Guide March 2020
α-opic equivalent daylight (D65) illuminance, lux
Light ConditionPhotopic
Illuminance (lux)
Roadway Luminance
(cd/m2)
S-cone-opic M-cone-opic L-cone-opic Rhodopic Melanopic
Indoor Exposure 200 lux -- 66.4 173.0 194.5 112.4 87.1
2100 K HPS - HIGH 1.8 lux 1.5 0.3 1.2 1.9 0.5 0.3
4000 K LED - HIGH 1.9 lux 1.5 0.6 1.6 1.8 1.1 0.8
4000 K LED - MED 1.4 lux 1.0 0.5 1.2 1.4 0.8 0.6
4000 K LED - LOW 1.1 lux 0.7 0.4 1.0 1.1 0.6 0.5
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Comparison of Consumer Electronic Devices to LED Road Lighting
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Integrating these value metrics into roadway lighting design
• Safety (Perceptions & Performance)
• Effects on Plants, Animals, & Insects
• Human Health
• Environmental Effects
• Energy Efficiency
Advancing Transportation Through Innovation
Dimming or change in spectra or both
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Evolution of Roadway Lighting Design
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Good Roadway Lighting Design is a Balancing Act
Public Perception
Security
Safety
Ecological Effects
Skyglow
Health Effects
Energy Usage
Max
imiz
eM
inim
ize
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Consider Light as a Medicine
• Right Type
• Right Amount
• Right Time
• Right Location
• Adaptive Lighting• Dimming during periods of low use
• Cambridge, MA
• Tucson, AZ
• San Jose, CA
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Value metrics for future
• How much light and what spectra are allowable• What are the thresholds for lighting impact
• What are the long term effects? How to quantify?
“To ask the right question is already half the solution of a problem.”— C.G. Jung