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OCR for page 30
30
· Pedestrian Detection Distance 7
The LEDs also had the shortest pedestrian detection
distance due to the high effective intensity of the light 6
Attention-Getting Rating
washing out the view of the pedestrian (Figure 17).
5 LED
The other (non-LED) warning lights had similar per- Low Beacon
Strobe
formances to each other with regard to pedestrian detec-
4 High Beacon
tion distance; however, the low-mounted beacons had
the highest mean distance. This result may be because the 3
lights and the illuminated tailgate provided a contrasting
background for the pedestrian's silhouette. 2
· Confidence Rating
The LEDs provided the highest confidence ratings due to 1
0 500 1000 1500 2000 2500
higher effective intensity; however, from an application
Form Factor Method
standpoint, the performance of every light was very high.
The low-mounted beacons provided higher confidence Figure 18. Daytime attention-getting rating by the
ratings than the high-mounted beacons of the same effec- light source effective intensity (17 scale).
tive intensity. This result was because the high-mounted
beacons were more affected by "daylighting" during the
uphill conditions. The low-mounted beacons had a higher discomfort glare
· Attention-Getting Rating rating than the high-mounted beacons with the same
The high effective intensity of the LEDs provided the effective intensity, probably because the light reflecting
highest attention-getting ratings (Figure 18). off the tailgate added an additional source of glare.
The low-mounted beacons provided higher attention- · Urgency
getting ratings than the high-mounted beacons (of the Higher effective intensity did not provide an additional
same effective intensity) and the strobes (which had a urgency benefit.
higher effective intensity). The added light reflection The rotating beacons and strobes yielded a higher rat-
from the tailgate may have increased the low-mounted ing with a less intense light because the flash patterns
beacons' visibility over the strobes. For the high-mounted appeared faster than the LEDs.
beacons, low contrast as a result of being viewed against
the sky is still a significant factor in the results. Discussion
· Discomfort Glare
As expected, the LEDs (which have the highest effec- The experiment has shown that many of the factors in-
tive intensity) resulted in the highest discomfort glare volved in the design and layout of a vehicle's warning-light
ratings (Figure 19). system influence the response of the driver to that vehicle.
350 9
Pedestrian Detection Distance (ft)
300 Low Beacon 8
High Beacon
Discomfort Glare Rating
Strobe
250 7
6
200
LED
5
150 LED
4 Low Beacon Strobe
100 High Beacon
3
50 2
0 1
0 500 1000 1500 2000 2500 0 500 1000 1500 2000 2500
Form Factor Method Form Factor Method
Figure 17. Pedestrian detection distance by the light Figure 19. Discomfort glare rating by the light source
source effective intensity (Form Factor method). effective intensity (19 scale).
OCR for page 31
31
The purpose of the dynamic experiment was to further re- · Lighting Characteristics
fine the requirements of the warning-light system in a driv- The effective intensity of the sources influenced the de-
ing environment with the addition of adverse weather con- tection of the pedestrian and the assessment of the light
ditions. The aspects of the warning-light system that must source glare. The higher effective intensity reduced the
be considered are the lighting layout, adverse weather in- ability of the driver to see the pedestrian and also resulted
fluences, further refinements of the lighting characteristics, in a higher discomfort glare rating.
and influence of other environmental factors such as ap- The vehicle detection distance was reduced for the LEDs
proaching vehicle glare. because of the system's longer flash duration. The double
flash of the strobes and the effective intensity changes of
· Lighting System Layout
the rotating beacon seem to have provided an additional
Separation of the warning-light system from the tail
clue to the nature of the lighting system.
lights of the vehicle aided in the identification of the
The urgency rating was also reduced for the LEDs. The
vehicle. Many participants indicated that tail lights
urgency of the lighting system also seems to be more
were the important cue for the vehicle identification
closely related to the apparent speed of the flashing.
distance.
Use of a double flash or a beacon seems to improve the
One of the difficulties with placing the warning-light
driver's response.
system high on the vehicle is that the lights may appear
against the sky. The lighting should be placed either such The use of a 360° light source close to the line of sight of
that the vehicle is behind the source or such that a back- the driver increased the experienced glare; it should be
ground is located behind the light in order to control avoided.
the contrast. · Other Environmental Factors
· Adverse Weather The presence of the opposing vehicle on the roadway re-
The influence of the rain and fog conditions did not seem duced the pedestrian detection distance by increasing
to significantly influence the participants' subjective the disability glare.
ratings of lighting system performance. The opposing vehicle also reduced the discomfort glare
The rain and fog significantly reduced the vehicle identi- ratings, because the warning-light systems are not as sig-
fication and pedestrian detection distances for all the light nificant a source of glare as the opposing headlamps.
sources and seemed to moderate the differences between The presence of the opposing vehicle did not affect the
the systems except for the LEDs. vehicle identification distance.
The LEDs resulted in much lower pedestrian detection The presence of other lighting systems, such as the road-
distances than the other systems. The LED system had way lighting experienced during the surprise trial, greatly
the highest effective intensity, which resulted in a larger reduced the discomfort glare rating of the warning-light
amount of light scatter observed by the approaching systems but did not change the urgency rating.
driver in rain and fog conditions. A higher effective-intensity light source may be required
It is expected that the effective intensity of the light would in the presence of roadway lighting, or in daylight con-
have to be limited to avoid the impact of light scatter ditions, as suggested by the lane-change distance results
under adverse weather. from the surprise trial.
