Session 11: Model Calibration, Validation, and Reasonableness Checks
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1 Session 11: Model Calibration, Validation, and Reasonableness Checks Source: NHI course on Travel Demand Forecasting (152054A)
2 Terminology Model Calibration Model Validation Special generators Reasonableness checksSensitivity checksSpecial generatorsScreen lines (some modelers do not think this is important)Is the model sensitive to policy options?
3 Key ConceptsNot enough attention on model evaluation and reasonableness checksChecks performed after each stepreduces error propagation
4 Information Requirements for Validation and Reasonableness Demographics and employmentHighway and transit networksBase year surveyBase year traffic counts
5 Sources of Error Network coding Sampling Computation Specification Data transferData aggregation
6 Documentation of calibration? Inputs and OutputsNumber and location of households and employment (demand)Socioeconomic DataComplete?Level of Detail?Transportation system(supply)Network DataReasonable?Methodology?Source?TDFModel SpecificationModel validation and calibrationTravelsurvey dataSensitive?Documentation of calibration?Valid for base year?Transportation systemperformanceCurrent?Reasonable?
7 Model Calibration and Validation IndependentData SetsFeedback LoopModel ValidationModel Application
8 Socioeconomic Data: Check Reasonableness of … Source for estimates and forecastsPopulation and household size trends (graph 1950 to present and check trend)Household income trends (graph as far back as this goes … 1990?)Dollar values used in forecast (use constant dollars)If used, trend of automotive availability (S curve?)Distribution of employment by type (basic, retail, service) over timeEmployees per household and per capita … rate of increase is decreasingHousehold and employment changes by zoneArea type (density) changes – are the growth areas reasonable?
9 Travel Survey Data Reasonableness Checks Types of survey conductedYear of surveyIf no survey (borrowed)Source of trip rates, lengths, TLFDIs area similarGeographic area?pop/HH/emp characteristics?Urban density and trans system?Trip chaining conventionCompare to similar regions and to sameregion in earlier times:Person trip rates by trip purposeMean trip lengths by trip purposeHBW longest? HBO shortest?TLFDs by trip purpose
10 Network Data Reasonableness Checks Facility types, level of detailSpeed and capacity look-up table (what LOS used for capacity?)Significant transportation projects – narrative?Plot (facility types, #lanes,speeds, area types)
11 Trip Generation Reasonableness Checks Trip production and attraction modelsForm?sensitivity?Trip purposes usedPerson trip or vehicle trip rates used?P&A balance ( ok)Special generators (be consistent in future model)
12 Trip Generation Calibration Typical Values Person trips per household: 8.5 to 10.5HBW person trips per household: 1.7 to 2.3HBO person trips per household: 3.5 to 4.8NHB person trips per household: 1.7 to 2.9HBW trips: 18% to 27% of all tripsHBO trips: 47% to 54% of all tripsNHB trips: 22% to 31% of all trips
13 Trip Distribution Reasonableness Checks Mean trip length (increasing or decreasing?)TLFDs
15 Mode Split Reasonableness Checks Automobile occupancy factors by trip purposeBasis? Constant?Form of mode split model?Variables included in the utility functions?Coefficients logical?IIA properties of LOGIT modelsMode share changes over timeMode share comparisons with other cities
16 Mode Split Calibration and Validation Advanced concepts needed to formulate and calibrate mode split modelsExperienced planning consultantCalibration tasks:Form of LOGIT modelVariables included in utility functionsCalibration of coefficients for utility function variablesTesting for IIA propertiesAnalysis of household survey dataAnalysis of on-board transit survey dataTotal highway and transit tripsRidership by route
17 Trip Assignment Reasonableness Checks Compare to see where adding capacity may helpAll-or-nothing assignmentEquilibrium assignmentVolume delay equation (BPR)Screen line volumesTime-of-day assignmentsLocal VMTEquilibriumAll orNothing
18 Trip Assignment Calibration and Validation Assignment calibration performedlastOverall VMT or VHT check40 to 60 miles per day per HH in large metro areas30 to 40 miles per day per HH in medium metro