1. CE 451 - Urban Transportation Planning and Management Iowa State University Calibration and Adjustment Techniques, Part 1 Source: Calibration and Adjustment of System Planning ModelsCalibration and Adjustment of System Planning Models Note: Date = 1990 (need to adjust for inflation, other changes)

2. Using cell phone and/or GPS location to determine travel patterns is nothing new. But leave it to Google to make it really easy - maybe too easy. http://googleblog.blogspot.com/2009/08/bright-side-of- sitting-in-traffic.html Adam Shell Office of Systems Planning Iowa Department of Transportation

3. CALIBRATION and VALIDATION are sometimes confused. Model development is sometimes called calibration or estimation as we are estimating parameters and constants for the particular model structure. estimating is a statistical process … want high correlation coefficients and significant parameter values can "import" a model - or borrow structure and parameters from a "similar" area VALIDATION is checking if the model is accurately estimating traffic volumes

4. check trip interchange (distribution) between large sections or quadrants need a survey; local knowledge of commute patterns helps compare traffic counts across screenlines (long lines, check major flows) cordon lines (surround a major generator, e.g. university, CBD...) cutlines (shorter, verify corridor flows, fine tuning) if "importing" should validate all borrowed parameters and constants

5. IT IS VERY IMPORTANT TO HAVE A GOOD COUNT PROGRAM DESIGNED TO SUPPORT VALIDATION!

6. The Calibration and Adjustment manual is not intended to replace good OD data, and is intended more for small urban areas. (and has some old data in it! – more recent data area available in the Barton-Ashman publication). Calibration deals with making your model replicate OD surveys (trip interchange) and validation is checking the model against ground counts. To "calibrate" the model, need an OD database from a survey. This is time consuming and expensive. Few, if any cities have developed OD databases since 1980, but many have updated old ones since then using a small survey (e.g. 1%)

7. To calibrate trip generation and trip distribution, sometimes we may use... - default values from past surveys - very limited new surveys - census journey to work data (CTPP?) IMPORTANT: keep parameters reasonable (e.g. don't use negative coefficients in regression models just because they provide the best fit. why???) If you think you need to use unintuitive parameters, check the whole process...

8. Calibration and Adjustment Steps: 1) verify network and socioeconomic data 2) run the model 3) develop region-wide values (e.g. trips/person, vmt/person) 4) compare region wide values with Appendix A values 5) develop screenlines and cutlines 6) compare model results with ground counts for crossings 7) determine problems (system level, local, combination) 8) modify one or more equations, parameters or variables according to chapters on: - networks - trip generation - auto occupancy - trip distribution - traffic assignment

9. Other chapters focus on: - transit - external stations - system vs. local changes - expected vs. required accuracy - conclusions - trouble shooting

10. Details 2. Network Errors 2.1 Centroid Connectors -rules of thumb: -all 4 sides -8-10 links per zone - check access - represent local streets - not connected to intersections - make sure they are not blocked by a physical barrier (river, etc.)

11. 2.2 Speed and Capacity - look up table (enables quick testing) - for smaller urban areas, some drivers use distance minimization (low frequency loads) - speed adjust (can lower the freeway speed if it is being overloaded – tweak?)

12. Des Moines Model Capacity Look-up Table

13. Des Moines Model Capacity Look-up Table (cont.)

14. 2.3 Intersection Penalties (check them!) - most congestion here - more important in sub-area modeling - turn penalties - account for congestion - speed volume function - can include delay on approach links - can do it manually for small networks -check for circuity (correct with small turn penalties!) -See TransCAD Manual B “Chapter 10: Traffic Assignment with Volume Dependent Turning Delays”

16. 2.4 Intrazonal times - increasing intrazonal trips (in distribution) decreases interzonal trips (useful if too many trips are being loaded on the network) - number of trips is a function of travel time (gravity model) - can adjust travel time on intrazonals - can adjust friction factor curve to produce more shorter trips (which intrazonals usually are) - definition of zones (size, land use) - should have less than 10,000 to 15,000 vehicles per day on centroid connectors

17. 3.1 Trip generation - socioeconomic data can be a source of error - initial step is to check system trip totals, compare w/ Table 4 and A1 and A2 (next pages) - if there is a problem, check the system number of dwelling units - still a problem?, check production/attraction rates

19. Table A2

20. From Minimum Travel Demand Model Calibration and Validation Guidelines for the State of TNMinimum Travel Demand Model Calibration and Validation Guidelines for the State of TN

22. 3.2 Income - be sure you are using “real” dollars

23. 3.3 P and A rates -Problems: old, borrowed, small survey - may work OK at the system level, but not for sub-areas - check system-wide values (see tables, next pages) - raise or lower trip generation rates - consider special generators - we have person trip by purpose, but can combine and check against vehicle rates (ITE) - later, screen line counts can be adjusted by varying trip generation rates (post assignment) - check cutlines and cordon counts -coordinate all of the above

27. home Non-

28. 3.4 Special generators -e.g. universities, airports, malls,... -Use ITE or survey

29. 3.5 trip balancing factors - initially, should be 0.9 to 1.1; if not, check your PA rates and socioeconomic data -NHB is usually out of balance 4.0 Auto occupancy - see table 6 and A9 (next pages … are these still good?)