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methods are introduced, the practicing community will face many uncertainties relating to needed data, model development procedures, and application software. There is also uncertainty about how consultants should be selected and used in developing advanced techniques. It will take time for the practitioners to become educated and comfortable with new methods. The TPB is planning to conduct a survey of 10,000 households in the coming year to obtain current travel behavior data. We plan to use the survey data to support the update of our trip- based models, and, in the longer term, to support the development of activity- based mod- els. While we can discuss the advantages of activity mod- els over conventional models, I still want to stress the point that no model will operate well if the inputs to the model are of poor quality. It is important to remember that the inputs to the model are critical to arriving at realistic results. We should ensure that adequate resources are focused not only on modeling improve- ments, but also on striving to improve input data to the model. Chuck Purvis The papers and presentations have been interesting andinformative. I would give the best paper award to Ram Pendyala and Chandra Bhat for their paper, âVali- dation and Assessment of Activity- Based Travel Demand Modeling Systems.â I also found the information on the work under way at the Denver Regional Council of Gov- ernments and the Sacramento Area Council of Govern- ments to be very interesting. We can all learn from their experiences as we move forward with model estimation with the next generation of activity- based models. I also learned about clock- time savings that one can accrue by freezing an activity- based model process after certain steps in the model application. One topic I would like to learn more about is the level of uncertainty in our activity- based models. We need to present a range of values to represent this uncertainty. I would also like to hear more about the validation of the synthetic population generation component. We do have multiple years of public use microdata sample data and we need to thoroughly test the population synthesizers using past census data and the new American Com- muters Survey that should be available this fall. I think training and education is the number one obstacle to advancing the use of activity models and other techniques. We also need a summary of the issues related to the non- market- segmented trip- based models, the market- segmented trip- based models, and the microsimulated models. We need a discussion of the issues related to ecological fallacies associated with moving from a naive segmentation to the full microsimulation. A second obstacle relates to the limited experience that we currently have with the use of activity models and other advanced techniques. Experience is limited at MPOs and in the consultant community. For widespread application of these techniques, we need widespread dis- semination of information on experiences with the use of different models. The Metropolitan Transportation Commission (MTC) held a peer- review panel funded through the Travel Model Improvement Program in December 2004. Our next activity was a model specification and training study. We are in the process of reviewing our specifica- tion plan. We have gone through some very intensive in- house training over the past few months. The MTC staff will estimate the activity- based model. We will use con- sultant assistance with the specification plan, the over- sight of staff estimation of the models, and the software construction after we are done with the estimated mod- els. We are using a work- sharing approach to these activ- ities. I am very excited about the process. The training effort focused on multimodal logit mod- els, nested logit models, destination choice models, esti- mation of daily activity patterns, interhousehold interaction models, and tour departure and duration choice models. This approach gives MTC staff a pride of ownership and an excellent understanding of the mod- els. This approach may not work for all MPOs, but for us, estimating the models in house and working in part- nership with consultants is an excellent way to imple- ment a new set of travel behavior models. I also have a concern over whether we should refresh our trip- based models. Our approach of using staff rather than consultants to implement activity- based models will probably take longer than relying totally on consultants. I think that in the end we will have a better model, a better process, and a better-trained staff. Aichong Sun Iappreciate the opportunity to provide a perspectivefrom a medium- sized MPO. Voters in Pima County, Arizona, recently approved an increase in the sales tax that is dedicated to transportation projects in the county. The sales tax is expected to generate approximately $2.1 billion over the next 20 years. We use a conventional four- step travel model at the Pima Association of Governments. We just completed a model update with the assistance of consultants. Three components were added to the model as part of this update. These components are a household model, a time- of- day model, and a mode choice model. The outputs of the household model include house- hold income, automobile ownership, and the number of workers. Previously, we could only model 24-hour traf- fic volumes. The time- of- day model allows us to model 65NEXT STEPS
