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66 I N N O VAT I O N S I N T R AV E L D E M A N D M O D E L I N G , V O L U M E 1 different times of the day, such as the morning and after- benchmark and compare different models to ensure that noon peak periods. The mode choice model is the most MPOs select a model that best meets their needs. important of the three components. Third, we are seeing changes in the types of questions We have been using a very simplistic approach to the in household travel surveys. Rather than just simply ask- land use elements in the model. We use data from local ing the standard questions related to individual travel jurisdictions on population, employment, school enroll- behavior, additional questions are being included to ment, land use, and other socioeconomic characteristics. obtain a better idea of why people are making certain The Maricopa Association of Governments in the travel choices. Phoenix area is leading an effort to develop a new land The reliability of the transportation system is becom- use model. The Pima Association of Governments will ing a more important issue. We are developing a regional be one of the major users of the new land use model. transportation plan in Portland. With limited funding We do not have any plans at this point to move toward for projects, congestion, especially in the peak periods, the use of activity-based or tour-based models, primarily will continue to be an issue in the area. A 20-minute trip because of budget, staffing, and data constraints. We do in the off-peak period typically takes 40 minutes in the have a number of surveys scheduled and we have an peak period. The consistency of the peak travel times is ongoing traffic count program. On an annual basis, we also an issue. Trip time reliability appears to be more conduct traffic counts at 380 sites and 16 intersections. important to commuters than the travel time. As a result, We also conduct regular vehicle classification counts. An trip time reliability is also becoming an important factor external station survey is scheduled for 2007. A travel in the decision-making process. We need to have trip speed and travel time savings survey using a Global Posi- time reliability in our modeling tools to provide accurate tioning System is also scheduled for 2007. We hope to information to decision makers. conduct another household travel survey in 2008. Another important issue is assignments under satura- I found the papers to be very interesting and learned a tion conditions. I was not able to attend the session good deal about the capabilities of activity-based models where this topic was discussed, but clearly traffic con- at the sessions. Given the resources to develop and gestion is a way of life in urban areas. As a result, assign- maintain activity-based models, however, we need to be ment techniques with saturation are very important. able to show that the results are superior to those pro- I would suggest using the word "challenges" rather duced by the traditional four-step model before we are than "obstacles" in describing the key issues we face in able to make a significant investment in these models. advancing the state of the practice. An important chal- lenge is that we need to be aware that activity-based Richard Walker models may produce different results than traditional four-step models. These differences may not be evident I have been fortunate to have had the opportunity to work with activity models throughout my career. Keith Lawton, formerly with Portland Metro, has been a in the base year, but the future year results from an activity-based model will be different from those obtained through a traditional four-step model. While it national leader in applying activity-based models. Hav- is to be expected that there will be differences, it can be ing worked extensively with activity-based models, I did a challenge to explain the reasons for these variations to not really learn anything new at the conference. A num- policy makers and other groups. We need to be very ber of important points were reinforced and expanded strategic in implementing activity-based models and in upon by speakers, however. presenting the results. I would like to highlight a few of the points made Another challenge relates to future survey methods. throughout the conference. First, "one size does not fit Issues related to cellular telephones versus land-line tele- all" in dealing with models, model forms, and the needs phones, freight data, and nonresponse levels all repre- of MPOs. Agencies should look at the issues in their sent challenges. We are working to update our regional areas, as well as their staff and financial capabilities freight data model. Obtaining accurate data on freight when determining the best models and techniques to use. movement at the zone level is difficult. The model approach for one MPO may be very different Guidelines at the federal level continue to change as a from the model approach for another MPO. result of SAFETEA-LU and other programs. Addressing Second, speakers described the different activity- new and modified guidelines and requirements related to based models available for practical application, as well travel forecasting for different programs and projects as those in the development stage. In considering an will continue to be a challenge. activity-based model, it is important to review the ele- It is also important to think about key elements with ments used in the models, the data needs, and the model the introduction of activity-based models. Examples of capabilities. We are at a point where we can establish a these elements include changes in coding, model run-