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used by the 26 MPOs in the state. There continues to be growing interest in rail freight operation simulation and inputâoutput and commodity flow models. National and statewide data sets need to be consistent with regional data sets. Regional data sets often suffer from the lack of consistency within the model itself or within the activity decision- making tree. As modelers, we face two important issues. The first issue is that we do not tend to talk about context. We need to establish the context within which the models are being applied. For example, regions are growing at different rates. The size of regions varies. Congestion lev- els are different and the air quality status may be differ- ent. Model applications may be used for new start projects, megaprojects, toll roads, and value- pricing projects. It is not fair to us as modelers to recommend model elements to a community if we do not first establish a context for the community. We also need to remember who the client is in the development and use of technical tools. If we as professionals do not do a good job of answering the questions, the political process will answer them for us. When most of us went to school, we were trained to help predict and analyze future assumptions. We were trained to inform the public of the consequences of spe- cific futures based on one set of demographics. We were trained to test alternative road and transit networks. We also learned to examine one road and transit network and test alternative demographics. Finally, we learned to examine alternative networks and alternative demographics. However, we live in a different world today. Elected officials are not modelers. Some policy makers in our region have suggested that we run our travel models backwards. This approach involves the transportation profession identifying the transportation networks, the transportation modes that should be built in various cor- ridors, and what projects should and should not be added to corridors so the region can sustain the demo- graphic forecasts. The DallasâFort Worth Metroplex is growing by about 1 million people every 7 years. Current trans- portation funding cannot keep pace with the needs of this increased population. Policy makers are looking at a variety of transportation options, including tolling, vari- able pricing, managed lanes, and commuter rail to accommodate the mobility needs of a region with a cur- rent population of 6.5 million that is continuing to grow at a rapid rate. The land use model starts with the residential location of the housing trip, rather than the trip distribution model, which picks the work place location of a specific trip. The model efforts under way in Denver, Colorado, focus on simultaneously calibrating the land use and the transportation elements. The model that is run back- wards is the land use model. Using a land use model starts with a need to know what the public really wants. 5OVERVIEW OF THE POLICY ISSUES MPO Local and State Decision Makers Citizens, Agencies Recommendations Application Guidelines Consultants, Researchers Technical Guidance Policy Guidance and Funding Congress, U.S. DOT, State DOT Implementation Partnerships: TRANSIMS MPOs/Private Single State-MPOs Peer Review TMIP Listserv Feedback FIGURE 4 Role of MPOs in the transportation decision-making process. Information System Land Use Model Travel Model Evaluation/Recommendations Implementation Input-Output Model FIGURE 5 Role of modeling in the implementation process.
