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Brief presentation delivered on Jan. 17, 2013 on the SFCTA's experience comparing commercial speed data to speed data collected using the traditional floating car method
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SAN FRANCISCO COUNTY TRANSPORTATION AUTHORITY
Testing and Validating Commercial Speed Data for CMP LOS Monitoring
The SFCTA’s Experience
Meeting at ACTC
January 17, 2013
2011 CMP Data Approach
LOS Methodology
• Based on mean segment speed for arterials and freeways
Data Collection Methodology
• Floating car used for reported speeds and LOS
• INRIX data analyzed on experimental basis
• Compared to floating car results
• Considered for future implementation
SAN FRANCISCO COUNTY TRANSPORTATION AUTHORITY 2
2011 CMP INRIX Coverage
SAN FRANCISCO COUNTY TRANSPORTATION AUTHORITY 3
SF CMP Network Commercial Data Sample Size
2011 CMP Data Comparison
Findings
• Difference in average speeds throughout CMP network
• Arterials: approx. 5% diff.
• Freeways: <9% diff.
• Indicated that “private commercial data would provide an
equally acceptable data source to meet the requirements
of the CMP legislation.”
SAN FRANCISCO COUNTY TRANSPORTATION AUTHORITY 4
Category
LOS Monitoring
Results
(Floating Car)
INRIX
Arterials (PM) 16.6 mph 17.5 mph
Freeways (PM) 31.4 mph 34.2 mph
2011 CMP Data Comparison
SAN FRANCISCO COUNTY TRANSPORTATION AUTHORITY 5
y = 0.9598x
R² = 0.691
0
10
20
30
40
50
60
70
0 10 20 30 40 50 60 70
INR
IX
Floating Car
Weighted Average Speed Plot (mph), 2011
n=213
2011 CMP Data Comparison
Distribution of Differences Between Means
SAN FRANCISCO COUNTY TRANSPORTATION AUTHORITY 6
63
51
45
21
17 14
2
0
10
20
30
40
50
60
70
<0.2 0.2 to 0.4 0.4 to 0.6 0.6 to 0.8 0.8 to 1 1 to 2 >2
Fre
qu
en
cy
of
Se
gm
en
ts
Difference / INRIX Std. Dev.
n=213
2011 CMP Weaknesses
Example: Duboce Ave below the Central
Freeway
• Floating Car mean speed: 18.5mph
• INRIX mean speed: 37.0 mph
Other challenging locations for private
commercial data:
• Downtown (canyon effect)
• Low sample size segments
SAN FRANCISCO COUNTY TRANSPORTATION AUTHORITY 7
Thanks Google!
2013 CMP Data Approach
LOS Methodology
• Still using mean segment speed for arterials and freeways
Data Collection Methodology
• INRIX as primary data source
• Limited number of floating car surveys
• Target locations where commercial data is least effective
SAN FRANCISCO COUNTY TRANSPORTATION AUTHORITY 8
SAN FRANCISCO COUNTY TRANSPORTATION AUTHORITY
Thanks!
Questions?
Daniel Tischler
dan [dot] tischler [at] sfcta [dot] org
(415) 593-1661
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