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An Empirical Investigation of the Impacts of Sun-Related Glare
on Traffic Flow
Benjamin Auffray, French Ministry of TransportationChristopher Monsere, Robert L. Bertini, Portland State University
Presented at the 87th Annual Meeting of the Transportation Research BoardJanuary 16, 2008
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Presentation Outline Motivation Site and Data Description Assumptions Analyses Results Conclusions
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Motivation Congestion What are the impacts of
environmental factors on traffic flow? Snow, wind and rain well- investigated Most research studies crash-related
factors Sun-related glare not studied
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Sun Glare Effect Physiological action
Two aspects : disability and discomfort
Heterogeneity of the reaction
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Methodology Select site(s) with known glare issues Collect archived traffic data Reconstruct sun position by time of day
and month Gather weather information Estimate likely glare-effect windows Compare data for evidence of effect
Statistical and traffic flow
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Site Description Located on
northound Interstate 5, Portland, Oregon
Approaching downtown Portland
Unique geometry
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Data Description Traffic Data : Loop
detectors record flow, speed and occupancy at 20-second intervals
Weather Data : Station located at the Portland International Airport and data are recorded hourly
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Available Data2005 2006
Available Days 275 264
Available Clear Days 99 92
Available Overcast days
115 116
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Assumptions Solar Angle : maximum
sun angle with potential influence on traffic
Weather Conditions : determination of sky coverage categories used
Traffic : Sorting method using speed and flow
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Data Cleaning Process
Creation of time window using sun charts
Sorting by different weather characteristics
Sorting by traffic state
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Sun Chart Use
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Available Data
Total 142 ,442
Sun Angle < than 15 °11 ,271
Sun Angle > than 15 °48 ,624
C lear Sky1 ,304
Overcast Sky6 ,654
C ongested198
U ncongested1 ,106
C ongested1 ,797
U ncongested4 ,857
C lear Sky7 ,991
Overcast Sky29,112
C ongested898
U ncongested7 ,093
C ongested3 ,011
U ncongested26,101
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Evidence of a Sun Related Glare Effect
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Statistical Results
Congested
Sun Angle < 15°
Clear Sky Mean (SD, n)
Sun Angle < 15°
Overcast SkyMean (SD, n)
Sun Angle > 15°
Clear SkyMean (SD, n)
Speed 31.09 (5.21, 200)29.33 (5.67, 1797)
33.32 (5.92, 898)
Volume 1,719 (202, 200)1,682 (195, 1797)
1,645 (249, 898)
Standard Deviation
5.22 (200) 5.67 (1797) 5.93 (898)
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Statistical Results
Free Flow
Sun Angle < 15°
Clear Sky Mean (SD, n)
Sun Angle < 15°
Overcast SkyMean (SD, n)
Sun Angle > 15°
Clear SkyMean (SD, n)
Speed57.90 (4.40, 1004)
57.31 (4.33, 4857)
55.92 (2.90, 7093)
Standard Deviation
4.41 (1004) 4.34 (4857) 2.91 (7093)
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Speed-Flow Relationship
Issue of drawing solid conclusions
Same global shape of the curve
Different characteristics
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Speed-Flow Regression
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Conclusions Evidence of a sun related glare effect
Impact on traffic flow
Impact on driver behavior
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Potential Future Research Expand the on-site investigation with
more field instrumentation
Repeat the investigation somewhere else
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Acknowledgments Oregon Department of Transportation Portland State University ITS Lab Robert Bertini and Christopher
Monsere Christine Buisson, ENTPE J. B. Lesort, INRETS
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Questions ?