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 checks
Sensitivity checks
Special generators
Screen lines (some modelers do not think this is important)
Is the model sensitive to policy options?

3. Key Concepts
Not enough attention on model evaluation and reasonableness checks
Checks performed after each step
reduces error propagation

4. Information Requirements for Validation and Reasonableness
Demographics and employment
Highway and transit networks
Base year survey
Base year traffic counts

5. Sources of Error Network coding Sampling Computation Specification
Data transfer
Data aggregation

6. Documentation of calibration?
Inputs and Outputs
Number and location of households and employment (demand)
Socioeconomic Data
Complete?
Level of Detail?
Transportation system
(supply)
Network Data
Reasonable?
Methodology?
Source?
TDF
Model Specification
Model validation and calibration
Travel
survey data
Sensitive?
Documentation of calibration?
Valid for base year?
Transportation system
performance
Current?
Reasonable?

7. Model Calibration and Validation
Independent
Data Sets
Feedback Loop
Model Validation
Model Application

8. Socioeconomic Data: Check Reasonableness of …
Source for estimates and forecasts
Population 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 time
Employees per household and per capita … rate of increase is decreasing
Household and employment changes by zone
Area type (density) changes – are the growth areas reasonable?

9. Travel Survey Data Reasonableness Checks
Types of survey conducted
Year of survey
If no survey (borrowed)
Source of trip rates, lengths, TLFD
Is area similar
Geographic area?
pop/HH/emp characteristics?
Urban density and trans system?
Trip chaining convention
Compare to similar regions and to same
region in earlier times:
Person trip rates by trip purpose
Mean trip lengths by trip purpose
HBW longest? HBO shortest?
TLFDs by trip purpose

10. Network Data Reasonableness Checks
Facility types, level of detail
Speed 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 models
Form?
sensitivity?
Trip purposes used
Person 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 10.5
HBW person trips per household: 1.7 to 2.3
HBO person trips per household: 3.5 to 4.8
NHB person trips per household: 1.7 to 2.9
HBW trips: 18% to 27% of all trips
HBO trips: 47% to 54% of all trips
NHB trips: 22% to 31% of all trips

13. Trip Distribution Reasonableness Checks
Mean trip length (increasing or decreasing?)
TLFDs

14. 1st iteration
Calibrate friction factors

15. Mode Split Reasonableness Checks
Automobile occupancy factors by trip purpose
Basis? Constant?
Form of mode split model?
Variables included in the utility functions?
Coefficients logical?
IIA properties of LOGIT models
Mode share changes over time
Mode share comparisons with other cities

16. Mode Split Calibration and Validation
Advanced concepts needed to formulate and calibrate mode split models
Experienced planning consultant
Calibration tasks:
Form of LOGIT model
Variables included in utility functions
Calibration of coefficients for utility function variables
Testing for IIA properties
Analysis of household survey data
Analysis of on-board transit survey data
Total highway and transit trips
Ridership by route

17. Trip Assignment Reasonableness Checks
Compare to see where adding capacity may help
All-or-nothing assignment
Equilibrium assignment
Volume delay equation (BPR)
Screen line volumes
Time-of-day assignments
Local VMT
Equil
ibrium
All or
Nothing

18. Trip Assignment Calibration and Validation
Assignment calibration performed
last
Overall VMT or VHT check
40 to 60 miles per day per HH in large metro areas
30 to 40 miles per day per HH in medium metro

20. Other Factors Impacting Forecasted Travel Demand
Telecommuting
Flexible work hours
HB business
Aging population
Internet shopping
Roadway congestion
New modes