Traffic Estimation with Space-Based Data

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Traffic Estimation withSpace-Based Data

• Mark R. McCord
• NCRST-F
• The Ohio State University
• Workshop on
• Satellite Based Traffic Measurement
• Berlin, Germany
• 9-10 September 2002

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Satellite Imagery forVehicle Identification

• High Resolution Required
• Cars 1m - 2m panchromatic
• Trucks 4m panchromatic

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• High Resolution
• gt Low orbits
• gt Limited temporal sampling
• (dynamic traffic)
• gt Long time scale, geographically
  extensive applications
• gt Traffic Monitoring
• Average Annual Daily Traffic (AADT)
• Vehicle Kilometers Traveled (VKT)

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Improved AADT and VKTEstimation from
High-Resolution Satellite Imagery

• Acknowledgments
• P. Goel, Z. Jiang, B. Coifman,
• Y. Yang,C. Merry, Past Students

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National, Regional Network Coverage AADT and VKT
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Average Annual Daily TrafficVehicle Kilometers
Traveled

• AADT Traffic on a highway segment
• AADTs ? S?1,365 V24s, ? / 365
• V24s, ? ? 24-hour volume, segment s, day ?
• VKT Travel over the network
• (avg daily) VKT Ss1,S Lengths AADTs

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Estimating AADT on System

• (Permanent) Automatic Traffic Recorders
• V24s, ?, ? 1, 2, , 365, ?s ? Spatr
• 3 segments equipped with PATRs
• gt Calculate AADTs ?s ? Spatr
• gt Estimate temporal variability
• (expansion factors)
• e.g., EF(?) EFMDm(?),d(?), m(?) 1,2, , 12
• 
  d(?) 1, 2, , 7

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Estimating AADT on System (cont.)

• Moveable ATRs (Coverage Counts)
• V24s, ?, V24s, ?1, ? ? 1, 2, ,
  364,?s?Smatr
• 33 segments per year
• gt Estimate AADTs ?s ? Smatr
• AADTests fV24s, ?, V24s, ?1, EF(?),
  EF(?1)
• e.g. AADTests V24s, ?/EF(?)V24s,?1/EF(?1)/2

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Estimating AADT on System (cont.)

• Unsampled Segments in Year, Suns
• (S Spatr ? Smatr ? Suns)
• AADTs ? Suns fAADTs, ?s ?
  Spatr?Smatr, ?s ? Suns
• e.g. AADTs ? Suns AverageAADTs, ?s ?
  Spatr?Smatr
• AADTs ? Suns fAADTs sampled in previous
  year, network growth factors

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AccuracySampling, Estimation MethodologyCostLar
ge Labor and Equipment Expenses
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Satellite Imagery

• Potential
• Added Data
• Off-the-Road
• Spatial Perspective
• Access of Remote Areas
• Difficulty
• Unfamiliar (Density Based)
• Potential Error (Short Interval
  Observation)

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Original Image
Binary Image
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• Flowest(x,t?t) Density(x?x,t)Velocity(x?x,t)
  
• Flowest(x,t?t) vph
• ?t short (3-15 minutes)
• V24,ests, ? fFlowest(x,t?t s,?), EFh(h(t))
• e.g., V24,ests, ? 24Flowest(x,t?t s,?) /
  EFh(h(t))
• EFh hourly expansion factor

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• V24,ests, ? fFlowest(x,t?t s,?), EFh(h(t))
• AADTimgs f V24,ests, ?, EFMDm(?),d(?)
• EFMD seasonal factor (month-of-year,
  day-of-week)

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Relative Error(AADT Image-based AADTTrue) /
AADTTrue AADTTrue ? AADTGround-based
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Relative Errors, RE

• N 18
• N(RE gt 0) 12
• N(RE lt 0) 6
• Sample Mean 0.03
• Sample St. Dev. 0.15
• RELATIVELY UNBIASED

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Relative Errors, RE

• Sample St. Dev. (w. mean 0) 0.15
• Maximum RE 0.34
• Lower RE with better AADTGr-based
• Equiv. Count Interval 0.6 12.6 mins
• SURPRISING, PROMISING PERFORMANCE

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RE Decreases with Increased Simulated Time
Interval
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NETWORK LEVEL ANALYSIS
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Computer Simulation

• Inputs
• Traffic Patterns
• AADT distribution, Link Lengths, EFM, EFD
• - Ground-Based Sampling
• Permanent ATRs (PATRs)
• Coverage Counts (MATRs)
• Satellite-Based Sampling
• Variability/Error/Random Terms
• Outputs
• - AADT and VKT (VMT) Estimation Error
• Ground-Based Data Only
• Satellite- and Ground-Based Combination

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Satellite-Based Sampling Physical Relations

• FCDlat1,lat2 2(1-Fnpgt)NPIXRESNORB
• Llat1,lat2i, NORB)10-3)/EARlat1, lat2
  (5)
•  
• NORB 8,681,665.8/ (RH)1.5 orbits/day
  (9)
•  
• H gt 200 km gt NORB lt 16.3 orbits/day
  (10)
•  
• H (FL/WPI)(RES)(103) km (12)
•  
• NORBgt8,681,665/((FL/WPI)max(RES(103)6371)1.5
  orb/day (14)
•  
• Vsg 0.4633(NORB) km/sec (17)
•  
• DBR 3.706(NORB)(NPIX)(10-3)/(RESCOMP)
  Mbits/sec (18)
•  
• (NPIX)( NORB) lt 269.8(RES)(DBRCOMP)max
  (20)

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Satellite-Based SamplingMaximal Coverage

• (P1) Max Z1NORBNPIXLlat1,lat2i,NORB
• NORB,NPIX,i
• s.t. 90 lt i lt 180
• 8,681,665.8/((FL/WPI)max RES(103)6371)1.5
• lt NORB lt 16.3
• 0 lt NPIX lt NPIXmax
• (NPIX)(NORB) lt 269.8(RES)(DBRCOMP)max

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Satellite-Based Sampling Daily Coverage vs.
Resolution and Inclination Angle
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Variability/Error/Random Terms

• Ground-based sample ?(gr)
• V24(gr)s,? AADTsEFMM(?)-1 EFDD(?)-1
• exp(?(gr) -? (gr)2/2),
• ?(gr) N(0, ?(gr))
• ?(gr) Daily deviation from deterministic
  model
• Satellite-based sample ?(sat)
• V24(sat)s,? AADTsEFMM(?)-1 EFDD(?)-1
• exp(?(sat) -? (sat)2/2),
• ?(sat) N(0, ?(sat))
• ?(sat) Error in Expanding Short-Duration
  Counts
• and Daily Variability

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Impact of Satellite Supply Equivalent
Satellite Coverage (ESC)
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Extensions

• More image- vs. ground-based comparisons
• Expansion of short-interval flows
• Improved hourly factors
• Quantification of uncertainty in sub-hour
  expansion
• Bayesian and model-based estimation
• Spatial correlations
• Satellite and air-based sampling strategies
• Other Uses of Volume Data
• Statewide truck OD estimation
• Screening tool growth factors, ground-based
  sample strategies
• Implementation strategies