HDM-4 Calibration Henry Kerali Lead Transport Specialist The World Bank
Jan 21, 2016
HDM-4 Calibration
Henry Kerali Lead Transport Specialist
The World Bank
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
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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
Bituminous Road Deterioration ..
Data & Calibration
• Need to appreciate importance of data over calibration
• If input data are wrong why worry about calibration?
D ata
C alib ra tion
'The D epth o f the S ea andthe H eight o f the W aves'
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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
Estimating Calibration Coefficients
Un-calibrated Calibrated
Actualdeterioration
Model
We attept tominimise the
"mistake"
Time
Ext
ent
of
Def
ect
(%)
Actual Progression
Pre
dic
ted
Pro
gre
ssio
n
Actual Progression
Pre
dic
ted
Pro
gre
ssio
n
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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
Calibration: Hierarchy of Effort
General PlanningQuick Prioritisation
Preliminary Screening
Coarse Estimates
Field Surveys
ExperimentalSurveys and
Research
Desk Studies
ResourcesRequired
Time Required
Weeks
Months
Years
Limited Moderate Significant
Project AppraisalDetailed Feasibility
Reliable Estimates
Research andDevelopment
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
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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
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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
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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
Sensitivity Classes
Impact Sensitivity Class Impact Elasticity
High S-I > 0.50
Medium S-II 0.20 – 0.50
Low S-III 0.05 – 0.20
Negligible S-IV < 0.05
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SensitivityClass2/
ImpactElasticity
Parameter Important forTotal VOC3/
Parameter Important forVOC Savings4/
S-I > 0.50 kp - parts model exponentNew Vehicle Price
kp - parts model exponentNew Vehicle PriceCSPQI - parts modelroughness termC0SP - parts model constantterm
S-II 0.20 - 0.50 RoughnessE0 - speed bias correctionAverage Service Life AverageAnnual UtilisationVehicle Weight
E0 - speed bias correctionARVMAX - max. rectifiedvelocityCLPC - labour model exponent
S-III 0.05 - 0.20 Aerodynamic Drag CoefficientBeta - speed exponentBW - speed width effectCalibrated Engine SpeedCLPC - labour model exponentC0SP - parts model constanttermCSPQI - parts modelroughness termCrew/Cargo/Passenger CostDesired SpeedDriving PowerEnergy Efficiency FactorsFuel CostHourly Utilisation RatioInterest RateProjected Frontal Area
Beta - speed exponentVehicle Age in kmC0LH - labour model constanttermLabour CostHourly Utilisation RatioBW - speed width effectsNumber of tires per VehicleNew tire CostLubricants CostCrew/Cargo/Passenger CostVehicle WeightNumber of Passengers
S-IV <0.05 All Other Variables All Other Variables
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Sensitivity Impact Parameter Outcomes Most Impacted Class Elasticity Pavement
Performance Resurfacingand Surface
Distress
EconomicReturn on
Maintenance S-I > 0.50 Structural Number 2/
Modified Structural Number2/
Traffic Volume
Deflection3/
Roughness
S-II 0.20 - Annual Loading
0.50 Age
All cracking area
Wide cracking area
Roughness-environment factor
Cracking initiation factor
Cracking progression factor S-III 0.05 - Subgrade CBR (with SN)
0.20 Surface thickness (with SN)
Heavy axles volume
Potholing area Rut depth mean Rut depth standard deviation Rut depth progression factor Roughness general factor
S-IV < 0.05 Deflection (with SNC) Subgrade compaction
Rainfall (with Kge) Ravelling area Ravelling factor
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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
Time Spend on HDM-4 Analyses
EstablishingReliable Input
Data40%
ModelCalibration
10%
Treatments,Triggers and
Resets20%
Running HDM-410%
Verification ofOutput20%
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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
For Further Information
• A guide to calibration and adaptation
• Reports on various HDM calibrations from:
www.lpcb.org
Discussions