Guidelines for Selection and Application of Warning Lights on Roadway-Operations Equipment Dr. Ronald B. Gibbons
Purpose • Develop guidelines for the selection and application of warning lights to improve the conspicuity and recognizability of roadway-operations equipment used for construction, maintenance, utility work, and other similar activities
Background There is a wide disparity in roadway maintenance vehicle warning lights This inconsistency raises problems of proper interpretation of their meaning No single study has tried to provide a comprehensive guideline for the marking of maintenance vehicles The impact of weather on the conspicuity and visibility of vehicles has not been investigated
Static Screening Experiment The screening experiment was designed to establish the impact of the lighting parameter factors on the conspicuity of vehicles The two primary questions were of interest in the Screening Experiment: • What are the critical factors from the lighting parameters that impact vehicle conspicuity and recognizability? • Which marking configurations are most effective and require further investigation in the performance experiment?
Static Screening Experiment Mixed-factor partial factorial design 24 participants • 12 male • 12 female
2 age groups: • 25 to 35 • 65+
82 conditions • 41 daytime • 41 nighttime
Independent Variables Intensity • High, Low
Format • LED, Halogen, Strobe, Beacon, Passive
Contrast • Daytime, Nighttime
Flash Pattern • Steady, Synchronized 1Hz, Asynchronous 1Hz, Asynchronous 4Hz
Color • Red, Amber, Blue, White
Position • Top-mounted, Shelf-mounted
Vehicle Configuration A surplus vehicle was obtained from the Virginia Department of Transportation A black panel was mounted on the rear of the vehicle (replaced the dump gate) Test lighting systems were mounted on this panel
Beacon Mounting
Dependent Variables Attention Getting • Night and Day • Rated on a seven point scale
Peripheral Detection Angle • Daytime only
Recognition • Participant was asked to identify the vehicle type from a list of vehicles • Nighttime only
Glare • Evaluated on a Scale of 1 to 9 (9 being unbearable) • Nighttime only
Color Peripheral Detection Angle by Color 90 80
Peripheral Angle
70 60 50
A
A
40
AB
30
B
20 10
C
0 Amber
Blue
Passive Color
Red
White
Glare by Color 9 8 A
7 Glare Rating
AB
6
BC C
5 4 3 2 D
1 Amber
Blue
Passive Color
Red
White
Impact of the Lamp Type and Location on the Peripheral Detection Task for Beacons 90 80
Peripheral Angle
70 60 LED Rotator Strobe
50 40 30 20 10 0 Shelf
Top Lamp by Location
Screening Experiment Summary Color • Amber provides the recognition of the vehicle as a maintenance vehicle
Intensity • Balance between glare and conspicuity • Different levels at night and day
Flash Pattern • Asynchronous Pattern seemed to have slight benefit
Light Source • LED or Halogen seemed not to be significant however the LED are more efficient and require a lower intensity
Lamp Location • Better performance was found when the light source appeared against the vehicle rather than the sky
Dynamic Performance Experiment In the dynamic performance experiment, the factors of ambient conditions, weather, visual complexity, light position, driver expectancy, and distraction were tested
All of the experiments were conducted on the VTTI Smart Road • Rain, Clear and Fog weather conditions • Day and Night • 4 Sessions were required for the experiment
The LED, Strobe and 2 Beacon conditions were used in the experiment An uniformed event was used at the beginning of the testing to test some of the characteristics
Performance Experiment Mixed-factor partial factorial design 32 participants • 16 male • 16 female
2 age groups: • 25 to 35 • 65+
116 conditions • 40 daytime • 76 nighttime
Independent Variables Warning Light • High-Mounted Beacon, Low-Mounted Beacon, Strobe, LED
Pedestrian • 40 ft, 80 ft
Glare • Glare, No Glare
Weather • Dry, Rain, Fog
Ambient Lighting • Day, Night
Dependent Variables
Uninformed Test • •
Lane Change Distance Attention-Getting
Smart Road Testing • •
• •
•
•
Vehicle Identification Distance • Participants stated when they were sure that they were approaching a vehicle Pedestrian Detection Distance • Distance at which a pedestrian beside the vehicle could be seen • Nighttime only Attention-Getting • 7 Point Scale Confidence • Rating from 0 to 100 • Daytime only Discomfort Glare • 9 Point Scale with 9 being the highest • Nighttime only Urgency • Rating from 0 to 100
Vehicle Setup The same dump truck from the Screening Experiment was used • The four lighting conditions were mounted on the vehicle
The system could be controlled by the driver All of the patterns were asynchronous with a 1 Hz frequency
Pedestrian Position The pedestrian was located at rear of the truck in the center of the approach lane • They were wearing Denim Scrubs and a retroreflective vest
Weather – Pedestrian Detection Pedestrian Detection Distance - Warning Light and Weather 500 450 400
Distance (ft)
350 High-Mounted Beacon Low-Mounted Beacon LED Strobe No Lights
300 250 200 150 100 50 0 Dry
Rain Weather
Fog
Impact of Appearance against Sky Attention-Getting Rating - Warning Light and Direction 7
Attention-Getting Rating (1-7)
6
5 High-Mounted Beacon Low-Mounted Beacon LED Strobe
4
3
2
1 Downhill
Uphill Direction
Photometric Comparison The light sources were photometrically characterized by NIST The photometric and experimental results were used to define limits for the photometric quantities allowed for the lighting system • This is a balance between the conspicuity measures and the glare rankings • The limits for daytime and nighttime Performance would be different • Glare limits are between 5 and 6 ranking level
Daytime Conspicuity Mean Daytime Attention-Getting Rating by Light Source Intensity for Panel Lights by Light Type and Color 7
6 Attention-Getting Rating (1-7)
Halogen Amber
5
LED Amber
Strobe Amber
4
Log. (Halogen Amber)
3
Log. (LED Amber)
2
Log. (Strobe Amber)
1 0
1000
2000
3000
4000
5000
Intensity (Form Factor Method)
6000
7000
Nighttime Conspicuity Mean Nighttime Attention-Getting Rating by Light Source Intensity for Panel Lights by Light Type and Color 7
6
Attention-Getting Rating (1-7)
Halogen Amber
5
LED Amber
Strobe Amber
4 Log. (Halogen Amber)
3
Log. (LED Amber) Log. (Strobe Amber)
2
1 0
1000
2000
3000
4000
5000
Intensity (Form Factor Method)
6000
7000
Glare Limits Mean Discomfort Glare Rating by Light Source Intensity for Panel Lights by Light Type and Color 8 7
Discomfort Glare Rating (1-9)
Halogen Amber
6
LED Amber
5
Strobe Amber
4
Log. (Halogen Amber) Log. (LED Amber)
3
Log. (Strobe Amber)
2 1 0
1000
2000
3000
4000
5000
Intensity (Form Factor Method)
6000
7000
Draft Intensity Limits Photometric Limits Light Source Halogen LED Strobe
Intensity (by Form Factor Method) Nighttime Daytime Minimum Minimum Maximum 3500 900 2200 4000 1650 3500 1200 2200
Dynamic Experiment Summary Lighting System Layout • The Lights should appear against a controlled background not the sky
Adverse Weather • LED systems had increased scatter and caused decreased detection distances
Lighting Characteristics • 360º Sources should be avoided close to the line of sight • Lighting Systems with a profiled output provided better vehicle identification
Other Factors • Other vehicles and roadway lighting will generally reduce the impression of glare from the lighting system
Guideline Development Draft Guidelines have been submitted with the report to NCHRP for their Review. The Guidelines have been developed based on the results of these experiments • The guidelines consider: • Safety Issues for both the driver and the vehicle • Vehicle Types and Usage • Environmental issues • Light Source selection
Review should be complete by the end of February 2008
Contact Any questions or comments associated with this project or the draft results should be directed to the National Cooperative Highway Research Program (NCHRP) • Program Manager: Amir Hanna •
[email protected] • (202) 334-1892
