Traffic Counts and

Travel Model Performance

A Presentationto the

TPB Technical Committee April 1, 2005

Item 9

Presentation to the TPB Technical Committee 4/1/05

2

Traffic Counts and Model Evaluation

The ‘Yardstick’ of Model Performance Regional/Jurisdictional VMT Screenline/Cutline Crossings

Air Quality Requirements VMT Tracking Emission Budgets

Increasing Specificity Sought AADT, AAWDT, Seasonal, Time of day, Classification, etc.

Presentation to the TPB Technical Committee 4/1/05

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Model Performance is Relative Performance is an Estimated-to-Observed Ratio

Regional, Subregional, Jurisdiction, Screenline, Link, … Performance Depends on Accuracy of Both Estimated

and Observed Figures A Balanced Understanding of Both Estimated and

Observed Figures is Critical to Validation

Presentation to the TPB Technical Committee 4/1/05

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Traffic Counts in the Region

Highway Performance Monitoring System (HPMS) is Primary Source of Count Data DDOT, MDSHA, VDOT, Local Jurisdictions

AADT (MD) / AAWDT (DC and VA) Coding Counts in the Highway Network

Historically a Manual Process Using Count Books/Maps More Recently Electronic Transfer Using Georeferenced Count

Data Bases and COG’s Transportation Data Clearinghouse Data Used ‘as is’; Maximum Link Coverage Sought

Presentation to the TPB Technical Committee 4/1/05

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Samples Designed for Statewide Traffic Estimates Permanent Counting Stations, Continuous Operation Program Count Locations; Short Count Duration, 3-year

Collection Cycle Adjustments Applied to Counts

Current-year Program Counts Annualized Non-Current Year Program Counts Adjusted to Current Year Partially Operational Permanent Counts Annualized “Manual Adjustments” made to compensate for Equipment

Failure, Construction, Safety Issues, etc. Adjustments based on Perm.Counts Statewide

HPMS Overview

Presentation to the TPB Technical Committee 4/1/05

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HPMS is not a count of traffic, per se-- HPMS is an annualized traffic volume estimate based on a statewide sample of a limited number of locations.

A Case Can be Made: Model Performance expressed as an ‘Estimated-to-Observed’ Ratio Should be Considered as an ‘Estimated-to-Estimated’ Ratio

When HPMS data is used for a specific metropolitan area, data noise is a potential issue.

Observations on the HPMS

Presentation to the TPB Technical Committee 4/1/05

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Issues for Transportation Modeling

Highway Network is an Approximation of the Physical Roadway System

Resolving AADT Figures to AAWDT is Approximate

Directionality of Counts is Suppressed With HPMS Data

Ground Count Highway Network Coding Practices Can Also Introduce Noise/Bias Into the Performance Statistics

Presentation to the TPB Technical Committee 4/1/05

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Daily VMT Over Timefor the Washington Region By State

0

10,000

20,000

30,000

40,000

50,000

60,000

70,000

1993 1994 1995 1996 1997 1998 1999 2000 2001 2002 2003

Year

VM

T (i

n th

ousa

nds)

MD

VA

DC

Presentation to the TPB Technical Committee 4/1/05

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Time Series VMT Changefor the Washington Region By State

-10.0%

-5.0%

0.0%

5.0%

10.0%

15.0%

20.0%

'93-'94 '94-'95 '95-'96 '96-'97 '97-'98 '98-'99 '99-'00 '00-'01 '01-'02 '02-'03

Year

Ann

ual G

row

th R

ate

DCMDVAAll

Presentation to the TPB Technical Committee 4/1/05

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Yr 2000 Validation Freeways RMSE Summary

Links Ave Obs Ave Est Diff. Pct PctVolume Range Count Volume Volume (Obs-Est) Diff. RMSE RMSE

1.00-9.99K 23 8.04 18.65 -10.61 -131.89 14.00 174.0510.00-19.99K 94 14.65 27.80 -13.15 -89.76 17.38 118.6620.00-29.99K 63 24.81 40.00 -15.19 -61.23 18.26 73.6230.00-39.99K 159 35.33 41.85 -6.52 -18.44 12.57 35.5740.00-49.99K 136 43.79 52.43 -8.64 -19.73 17.24 39.3750.00-59.99K 90 54.20 65.33 -11.13 -20.54 15.57 28.7460.00-69.00K 113 64.68 65.88 -1.19 -1.85 14.96 23.1370.00-79.00K 84 73.62 76.55 -2.93 -3.98 17.10 23.2380.00-89.99K 78 84.62 81.81 2.81 3.32 15.41 18.2190.00-99.99K 90 94.89 90.64 4.24 4.47 15.23 16.05

100.00-109.99K 67 104.63 101.93 2.70 2.58 13.30 12.71110.00-119.99K 35 115.66 110.71 4.94 4.27 18.58 16.06120.00-129.99K 20 125.70 111.05 14.65 11.65 21.60 17.19130.00-139.99K 20 139.90 104.05 35.85 25.63 39.51 28.24Subtotal: 1,072 60.24 64.03 -3.79 -6.30 16.59 27.54

Presentation to the TPB Technical Committee 4/1/05

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Updated Traffic Volume Estimates for V2.1.D Model Performance Tests

Review Traffic Volume Data/ Estimates for all jurisdictions in the metropolitan Washington region (MSA).

Link AAWDT Traffic Volume Estimate only to the network link where the Program or Permanent Counting Station was located (i.e. no carrying forward or averaging volume estimates for adjacent links).

Identify all Program and Permanent Counting station locations where actual traffic count data was collected in Year 2000.

Identify all Permanent Counting Stations that were operational in Year 2000.

Presentation to the TPB Technical Committee 4/1/05

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All Program and Permanent Counting Locationswith Actual or Factored Daily Traffic Volume Estimates for Year 2000

Presentation to the TPB Technical Committee 4/1/05

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All Program and Permanent Counting Locationswith Actual Traffic Count Data Collected in Year 2000

Presentation to the TPB Technical Committee 4/1/05

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All Operational Permanent Counting Station Locations in Year 2000

Presentation to the TPB Technical Committee 4/1/05

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Performance Test Results

Sample Description Obs. RMSE %RMSE R2

V2.1D#50 Model Validation 11,004 8.01 47.21 0.84Permanent Station and Program Counts - 2,953 7.12 44.89 0.89Permanent and Actual Program Counts 1,194 5.8 40.33 0.92Permanent Counting Stations 68 6.65 18.04 0.96

Presentation to the TPB Technical Committee 4/1/05

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Validation E/O Scatterplots11,004 Observations

Plot of Estimated and Observed Year 2000 Link Volumes V2.1D#50 Validation Network

(Entire Modeled Area / 11,004 Obs. )

Linear Model:y = 0.93x + 2.34

R2 = 0.84

0

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160

0 20 40 60 80 100 120 140 160

Observed Volume (in 000s)

Estim

ated

Vol

ume

(in 0

00s)

Est vs Obs Line of perfect agreement Linear (Est vs Obs)

Presentation to the TPB Technical Committee 4/1/05

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Permanent /Actual & Factored Program Counts 2,953 Observations

Scatterplot of Estimated and Observed Year 2000 Link Volumes(All Program/Permanent Counts - 2,953 Obs

MSA Only/1.05 Ftr for ADT-to-AAWDT Conversion

Linear Model:y = 0.97x + 1.53

R2 = 0.89

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0 20 40 60 80 100 120 140 160

Observed Volume (000s)

Estim

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Vol

ume

(000

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Est vs Obs Line of perfect agreement Linear (Est vs Obs)

Presentation to the TPB Technical Committee 4/1/05

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Permanent /Actual Program Counts 1,194 Observations

Scatterplot of Estimated and Observed Year 2000 Link Volumes(Permanent & Program Counts Collected in 2000 - 1,194 Obs)

MSA Only/1.05 Ftr for ADT-to-AAWDT Conversion

Linear Model:y = 1.00x + 1.24

R2 = 0.92

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0 20 40 60 80 100 120 140 160

Observed Volume (000s)

Estim

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Vol

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Est vs Obs Line of perfect agreement Linear (Est vs Obs)

Presentation to the TPB Technical Committee 4/1/05

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Permanent Count Stations68 Observations

Scatterplot of Estimated and Observed Year 2000 Link Volumes(All Permanent Count Stations - 68 Obs.)

MSA Only/1.05 Ftr for ADT-to-AAWDT Conversion

Linear Model: y = 0.97x + 2.18

R2 = 0.96

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Observed Volume (000s)

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(000

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Est vs Obs Line of perfect agreement Linear (Est vs Obs)

Presentation to the TPB Technical Committee 4/1/05

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Conclusions Model Performance Improves with Higher Quality Counts

Metropolitan areas using statewide counting program data should expect count accuracy limitations-- especially multi-state areas. Consider metropolitan samples?

Expect scatterplot outliers, seek explanations

Performance problems does not equate to model problems.