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11 th National Planning Applications Conference

11 th National Planning Applications Conference. Topic: Statewide Modeling Validation Measures and Issues Authors: Dave Powers, Anne Reyner, Tom Williams, Paul Hershkowitz, Rob Bostrom Date: May 9, 2007. Modeling Issues. Statewide Modeling Objectives

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11 th National Planning Applications Conference

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  1. 11th National Planning Applications Conference Topic: Statewide Modeling Validation Measures and Issues Authors: Dave Powers, Anne Reyner, Tom Williams, Paul Hershkowitz, Rob Bostrom Date: May 9, 2007

  2. Modeling Issues • Statewide Modeling Objectives • Forecast major intercity volumes and roadway deficiencies • Estimate urban external-internal and through volumes • Freight transport growth and potential for intermodal diversion • Evaluate major travel corridor improvements • Urban bypass • Intercity corridor

  3. Modeling Issues • Off- Model Traffic • Urban intrazonal / local private vehicle • Rural local private vehicle • Freight intra-county • Commercial vehicles

  4. Modeling Issues • Observed Traffic Counts • Primary independent validation criterion • Vehicle class not universally available • Estimated traffic volumes • Geographically extrapolated traffic volumes

  5. Modeling Issues • Travel Demand Survey Data - Person • National Samples – not necessarily representative at the state level • Not comparable to traffic counts • Add-on samples can expand usefulness • Only source of intercity trips

  6. Modeling Issues • Travel Demand Inventory - Freight • Inter-county, large vehicle only • Requires extensive review for reasonableness • Requires conversion of tonnage to vehicles • Requires estimation of empty vehicle movements • Comparison to counts problematic

  7. Modeling Issues • Data Checking – Traffic Counts • Focus on rural higher functional classes • Eliminate urban influence • Review spatial and temporal consistency • Eliminate inconsistent and/or estimated/transferred counts

  8. 2003 vs 2006 Counts

  9. Modeling Issues • Data Checking – Person Travel Surveys • Review sample size by household categories • Compare trip rates, distribution characteristics across household categories • Supplement with similar state data if necessary

  10. Modeling Issues • Data Checking – Freight Flow Inventory • Compare flow origins/destinations with development inventories • If available, compare multiple year data • Major flow desire lines - review with knowledgeable state staff • Review load factors • Review implied empty backhaul factors • Assign and compare VMT and traffic on major roadways

  11. Modeling Issues • Validation Reasonableness Tests – Person Travel • Statistical correlation of model dependent and independent variables • Household trip rates • Proportion of trips by purpose / length • Average trip length / trip length distribution • Compared against model development data

  12. Modeling Issues • Validation Objective Tests – Person Travel • VMT by major functional roadway class • Volumes across major rural screenlines • Volumes at major state boundary crossings • Volumes along Interstate and other major roadways • RMSE and individual count deviation analysis • Identification and explanation of outliers

  13. Validation Screenlines - Mississippi

  14. Validation Screenlines - Kentucky

  15. Modeling Issues • Validation Reasonableness Tests–Freight • Statistical correlation of model dependent and independent variables • Tonnage by commodity type, and internal/external orientation • Replication of special generator origins/destinations • Inter-district flows • Average trip length / trip length distribution • Load factors / empty backhaul rates • Compared against model development data

  16. Modeling Issues • Validation Objective Tests – Freight • VMT by major functional roadway class • Volumes across major rural screenlines • Volumes at major state boundary crossings • Volumes along Interstate and other major roadways • RMSE and individual count deviation analysis • Identification and explanation of outliers

  17. Percent Deviation for Validation Links - Mississippi

  18. Percent Deviation for Validation Links - Kentucky

  19. Modeling Issues • Validation Expectations • Recognize limitations of source data • Focus on rural areas / higher functional classes • Quantitative comparisons will be less accurate than experienced with urban models • Validation quality may vary depending on model complexity, state development/road system complexity and traffic counting system

  20. Modeling Issues • Lessons Learned • Spend time and effort to fully understand assumptions and estimation procedures present in traffic counts • Spend time and effort to get input person and freight data as free from logical inconsistencies as possible • Focus model calibration and objective validation tests on facility types/volume groups where a statewide model can be reasonably expected to perform accurately

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