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