HDM-4 Calibration

1. HDM-4 Calibration Henry Kerali Lead Transport Specialist The World Bank

2. How Credible are HDM-4 Outputs? • Depends on Level of Calibration (controls bias) • Depends on accuracy and reliability of input data (asset & fleet characteristics, conditions, usage) • HDM-4 has proved suitable in a range of countries • As with any model, need to carefully check output with good judgement

3. Approach to Calibration • Input data • Must have a correct interpretation of the input data requirements • Have a quality of input data appropriate for the desired reliability of results • Calibration • Adjust model parameters to enhance the accuracy of its representation of local conditions 3

4. Bituminous Road Deterioration ..

5. Data & Calibration • Need to appreciate importance of data over calibration • If input data are wrong why worry about calibration?

6. Calibration Focus • Pavement Deterioration & Works Effects • Reflect local pavement deterioration rates and sensitivity to factors • Represent maintenance effects • Road User Effects • Predict the correct magnitude of costs and relativity of components - data • Predict sensitivity to changing conditions - calibration 5

7. Model We attept to Defect (%) Extent of minimise the "mistake" Actual deterioration Time Predicted Progression Predicted Progression Actual Progression Actual Progression Estimating Calibration Coefficients Un-calibrated Calibrated

8. Important Considerations • Calibrate over full range of values likely to be encountered • Have sufficient data to detect the nature of bias and level of precision • High correlation (r 2) does not always mean high accuracy: can still have significant bias • Primary aim: minimize bias 15

9. Calibration: Hierarchy of Effort

10. Calibration Levels • Level 1: Basic Application • Addresses most critical parameters • ‘Desk Study’ • Level 2: Verification • Measures key parameters • Conducts limited field surveys • Level 3: Adaptation • Major field surveys to requantify relationships • Long-term monitoring

11. Level 1 - Application • Required for ALL HDM analyses • Once-off ‘set-up’ investment for the model • Mainly based on secondary sources • Assumes most of HDM default values are appropriate 10

12. Level 2 - Verification • Make measurements to verify and adjust predictions to local conditions • Requires moderate data collection and moderate precision • Adjustments entered as input data, typically no software changes 11

13. Level 3 - Adaptation • Comprises: • Structured research, medium term • Advanced data collection, long-term • Evaluates trends and interactions by observing performance over long time period • May lead to alternative locally derived relationships/models 12

14. Sensitivity Classes

15. 21

16. 22

17. Can We Believe HDM-4 Output? • Yes, if sufficiently calibrated • HDM-4 has proved suitable in a range of countries • As with any model, need to carefully scrutinize output against judgement • If unexpected predictions occur, check: • Data used • Calibration extent • Check judgment of the expert 23

18. Model Calibration 10% Establishing Verification of Reliable Input Running HDM-4 Output Data 10% 20% 40% Treatments, Triggers and Resets 20% Time Spend on HDM-4 Analyses

19. Can We Believe HDM-4 Output? • Yes, if sufficiently calibrated • HDM-4 has proved suitable in a range of countries • As with any model, need to carefully scrutinize output against judgement • If unexpected predictions occur, check: • Data used • Calibration extent • Check judgment of the expert 23

20. For Further Information • A guide to calibration and adaptation • Reports on various HDM calibrations from: www.lpcb.org

21. Discussions