1. 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

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