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MEASURING PERFORMANCE ON INTERRUPTED FLOW
FACILITIES WITH GPS PROBE AND BLUETOOTH TRAFFIC
MONITORING DATAReuben M. Juster, EIT
Stanley E. Young, P.E., Ph.D.
Elham Sharifi, Ph.D.
CATTworks
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Vehicle Probes
• Alternative source of travel time data
• Third party vendors aggregate highway vehicles’ travel data
• Many different devices within or embedded in vehicles transmit the data
• Aggregated data is usually cleaned to get one reading per segment of roadway per time period
• Data available to users through web-interface / API
Car Manufacturers
Fleet Operators
Phone Manufacturers
Third Party Vendor
Cleaning
Us
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Applications
Operations Planning
Traffic Management Centers
Picture Sources: WSDOT, VDOT, Creative Loafing ATL, Maryland SHA, FHWA
Traveler Info Performance MonitoringInvestment Justification
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Not All Probe Data is Created Equal
• Probe data was first used for freeway-based applications
• Probe data users became interested in arterial-based applications
• The I-95 Corridor Coalition Vehicle Probe Project’s (VPP) validation program accessed the accuracy of the probe data
• Freeway data is generally more accurate than arterial data for several reasons
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Fundamental Facility Differences
Freeways (Uninterrupted)
• High volumes
• Continuous Flow
Arterials (Interrupted)• Lower volumes
• Interrupted flow
• Red lights
• Driveways
• Adjacent land uses
• Not all arterials data is created equal
• Vary by volume, signalized intersections, driveways, geometry
• Mobility Vs. Accessibility
• Which arterials can have probe data to derive performance measurements?
Driveway
IntersectionInterrupted
Uninterrupted
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VPP Validation
• Contract requires vendors to meet certain quality metrics
• This requires frequent validation studies on representative corridors to ensure that data meets metrics
• For freeways these metrics include Average Absolute Speed Error (AASE) and Speed Error Bias (SEB)
• These metrics work well for a uni-modal freeway travel time distributions, but not multi-modal arterial travel time distributions
Picture Sources: BTS, FHWA
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Alternate Validation Method (1/2)
09/02 09/09 09/16 09/23 09/300
5
10
15
Date/Time
Trav
el T
ime
- Min
utes
Northbound
Traversals
Outliers
09/03/12 09/05/12 09/07/12 09/09/12 09/11/12 09/13/12 09/15/12 09/17/12 09/19/12 09/21/12 09/23/12 09/25/12 09/27/12 09/29/120
5
10
15Travel Time Plot - US Route 1 NB - between Telegraph Road and Fairfax County Parkway
Date & Time
Tra
vel T
ime (
min
ute
s)
Score > 25
BTM ^ VPP v
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24 Hour Overlay Plot
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Alternate Validation Method (2/2)
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The Whole View
15%1.7
minutes
95%
7.7
minutes
𝑃𝑇𝐼 =95𝑡ℎ 𝑃𝑒𝑟𝑐𝑒𝑛𝑡𝑖𝑙𝑒
15𝑡ℎ 𝑃𝑒𝑟𝑐𝑒𝑛𝑡𝑖𝑙𝑒=
7.7
1.7= 4.5
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Example 1 Corridor Description
• US-1, Mercer County, New Jersey (Princeton)
• 6-8 lanes total
• <1 Signal per mile, 3.2 miles long
• Grade separate interchanges
• Minimal access points
• Resembles a freeway
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Example 1 Comparison
VPP
BTM
0 2 4 6 8 10 12 140
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
Travel Time - Minutes
Per
cent
ile
Travel Time CFD Diagram
12AM 3AM 6AM 9AM 12PM 3PM 6PM 9PM 12AM0
2
4
6
8
10
12
14
Hour of Day 0-24
Trav
el T
ime
- M
inut
es
Hourly Overlay Scatterplot
PTI = 2.1
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Example 2 Corridor Description
• US-130, Burlington County, New Jersey
• 6 lanes total
• 2 Signals per mile, 1.5 miles long
• Multi-cycle signal failures
Signalized Intersection
Grade-separate interchange
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Example 2 Comparison
0 1 2 3 4 50
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
Travel Time - Minutes
Pe
rce
ntil
e
Travel Time CFD Diagram
12AM 3AM 6AM 9AM 12PM 3PM 6PM 9PM 12AM0
0.5
1
1.5
2
2.5
3
3.5
4
4.5
5
Hour of Day 0-24
Tra
vel T
ime
- M
inu
tes
Hourly Overlay Scatterplot
VPP
BTM
PTI = 1.4
PTI = 2.5
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Recommendations
Arterials likely to have accurate probe data
Arterials possibly to have accurate probe data
Arterials unlikely to tohave accurate probe data
• AADT >40000• 2+ lanes each
direction• <= 1 signals per mile• Principal Arterials• Limited Curb cuts• Confidently
characterize congestion and performance measures
• AADT 20K to 40K• 2+ lanes each direction• 1 to 2 signals per mile• Minor Arterials (HPMS) • Some segments work
(likely), others fail (unlikely)
• No cycle failures• Should be reviewed to
see effectiveness of probe data
• Low volume, AADT <20K
• >=2 signals per mile• Major collectors
(HPMS)• Probe data not
recommended• Frequent cycles
failures• Use re-identification
for performance monitoring
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Future
• Probe data will improve with:
• Larger sample sizes
• Better processing (point pairing as opposed to instantaneous)
• Improved segmentation (already happening)
• Arterials that previously did not have accurate probe data may have accurate probe data (check every 18 to 24 months)
• In the mean time, verify validity if unknown
• Use the whole spectrum of the travel time distribution