3M - The Legibility of Traffic Signs under LED Headlight Illumination

Hugo Bruggeman 3M Company St. Paul Transportation Safety Division Laboratory

History of Vehicle Headlamps in Europe (ECE) Halogen H4 Diffuser Lens 1000 Lumen

LED Projector Lens 2000 Lumen

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Halogen H7 Reflector Type 1500 Lumen

HID (Xenon) Projector Lens 3200 Lumen

History of Vehicle Headlamps in Europe (ECE)

Typical ECE passing beam light distribution / HID Projector Lens / Model Year 2015 © 193M April 2022 . All Rights Reserved.

History of Vehicle Headlamps in the US

‚Visually Optically Aligned‘ VOA headlamp with sharp ‚cut-off‘ line, similar to ECE headlamp > Significantly less illumination for traffic signs © 193M April 2022 . All Rights Reserved.

Vehicle Trends in Germany and US SUVs • In 2021, 25% of new vehicle registrations in Germany are SUV • 56% of US Vehicles are Trucks / SUV

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LEDs • In 2021, 8 of 11 of Germany’s best selling vehicles come standard with LED Headlamp (Source: Kraftfahrtbundesamt) Rank

Model

Headlamp (standard)

Type

1

VW Golf

LED

Car

2

VW T-Roc

LED

SUV

3

VW Tiguan

LED

SUV

4

Opel Corsa

Halogen

Car

5

VW Up

Halogen

Car

6

VW Passat

LED

Car

7

Mini

LED

Car

8

BMW 3 Series

LED

Car

9

Skoda Octavia

LED

Car

10

Fiat 500

Halogen

Car

11

Tesla Model 3

LED

Car

Legibility of Retroreflective Traffic Signs

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Change in Headlamp Light Distribution • Passing Beam > 2019 LED lamps illuminate the roadway at higher levels than 2011 lamps • LEDs reduce illumination of typical sign positions while minimizing glare to other users on the roadway 2011

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2019 -LED

Contour plots of Log2 transformed luminous intensity distributions (log2*cd)

Impact of LED Headlamps on Sign Legibility • How much have sign illumination levels changed over the past decade?

• Is the change different for the 2019 LED lamps vs compared to the 2019 Halogen lamps?

• To analyze this, we ran simulations for UMTRI 2011 and 2019 matrices (25%tile) with prismatic retroreflective sheeting conforming to ASTM D4956 Type XI standard UMTRI Report: https://deepblue.lib.umich.edu/bitstream/handle/2027 .42/154777/UMTRI-2019-5.pdf © 193M April 2022 . All Rights Reserved.

3M Research Synopsis: https://multimedia.3m.com/mws/media/1775333O/lo w-beam-headlight-study-summary.pdf

Change in Headlamp Light Distribution Circles mark the location where signs are positioned • Overhead • Left shoulder • Right shoulder

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2011

Change in Headlamp Light Distribution Circles mark the location where signs are positioned • Overhead • Left shoulder • Right shoulder

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2019 LED

Traffic Sign Illumination US Beams 2011

• Similar illuminance curves for different vehicle types • Sign illumination levels increase during approach • High illumination levels for right shoulder sign • Low illumination levels for overhead sign

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Distance: 180m

150m

120m

90m

Reduced Illumination Levels for 2019 headlamps

…especially for Halogen lamps

Distance: 180m 150m 120m 90m © 193M April 2022 . All Rights Reserved.

180m 150m 120m 90m

180m 150m 120m 90m

Retroreflection and Vehicles VW Tiguan II vs.

VW Golf VIII

• more intensity in the center of the cone • larger vehicles receive less light • SUV and Truck Drivers in a disadvantaged position

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Traffic Sign Luminance Curves for 2011 A driver of a sedan or light truck benefits from increasing luminance levels A driver of a heavy truck may suffer from decreasing luminance levels Luminance curves for a heavy truck are decreasing because its driver is seated further above the headlights which is a disadvantaged position (larger observation angle).

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Distance: 180m

150m

120m

90m

Lower Luminance Curves for 2019

…even worse for Halogen lamps

Distance: 180m 150m 120m 90m © 193M April 2022 . All Rights Reserved.

180m 150m 120m 90m

180m 150m 120m 90m

Traffic Sign Legibility - 2011 vs 2019 Lamps • People differ in their luminance "needs" or demands.

• People who benefited from the increasing luminance levels under 2011 lamp illumination may find it more difficult to read signs under 2019 lamp illumination.

• In some cases, the change to lower luminance levels may mean that a driver is no longer able to read a sign under 2019 lamp illumination.

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Conclusions • Lower levels of traffic sign-illumination for 2019 headlamps compared to 2011 headlamps • Reduction may adversely impact drivers who have higher luminance needs, including some of the elderly drivers • Reduction is somewhat less for LED lamps than for Halogene lamps

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Conclusions Road administrations may consider upgrading to Class 3 retroreflective traffic sign sheeting in Full-cube technology The higher levels of retroreflection combined with the wider cone of retroreflection of full cube sheeting may mitigate the impact of the reduction in sign illumination with LED lamps 2011

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2019 -LED

Thank You Visit us at Intertraffic Amsterdam 29 MAR – 1 APR 2022, Hall 1, booth 01.253