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. 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

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. 5 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

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

8. 15 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

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. 10 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

12. 11 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

13. 12 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

14. Sensitivity Classes

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17. 23 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

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

19. 23 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

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

21. Discussions