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Traffic Forecasting in a Visioning Workshop Setting Don Hubbard, Fehr & Peers Associates V isioning workshops have become a vital tool in scrutinize inputs, analyze outputs, and, if necessary, per- regional planning. Unfortunately, traffic forecasting form additional model runs. Models are usually designed has played only a small role in these workshops even to accommodate detailed changes to networks or model- though traffic congestion is often viewed as a critical long-term ing parameters and to provide a rich assortment of issue. This creates the danger of a consensus forming in a work- potential outputs. In other words, their normal operat- shop around a vision that traffic modelers later declare is ing environment is completely unlike a public workshop. unworkable from a traffic standpoint. A disconnect of this kind A workshop model must produce sensible results can lead to one of two undesirable outcomes: 1) the agency within 15 min of receiving inputs from the participants-- abandons the consensus vision, in which case the workshop anything longer will make for unreasonably long work- participants rightly wonder whether their views are being taken shops and/or loss of interest by participants. Included in seriously, or 2) the agency is stuck trying to implement the that 15 min is whatever processing is needed to compute unworkable. One way to ensure that the consensus forms key indicators and report the results, which may take around a workable vision is to perform traffic forecasts during the form of printed reports or figures projected on a the workshop and give participants immediate feedback as to screen, plus time the operator needs to analyze and the likely consequences of their plans, allowing them to adjust interpret the results. There is not enough time to rerun their plans accordingly. the model if something goes wrong, so the inputs must This approach was successful in visioning workshops be prepared correctly the first time. Moreover, the sponsored by the Council of Governments for San Luis model must be robust enough to produce logical results Obispo County, California (SLOCOG), and the Sacra- for a wide range of input values, because it is difficult to mento Area Council of Governments (SACOG). These predict what sort of proposals will arise during a public are believed to be the first public workshops to forecast workshop. traffic in real time. The experiments used different mod- Fortunately, the outputs needed from a workshop els and approaches, both of which provide important model are much simpler than in a traditional model lessons for agencies that may want to play a role in application. Public participants have neither the time nor visioning exercises. the training to sort through long tables of subtle indica- tors; they prefer results expressed in a few easily under- stood numbers or figures. This greatly simplifies the GENERAL REQUIREMENTS FOR modeling task because it allows a modeler to pick a few WORKSHOP MODELS key indicators and then eliminate any model components that do not contribute to those outputs. For example, a Travel demand models are typically designed to be used workshop model might report the regional mode split in a private, unhurried setting with ample opportunity to but is unlikely to report patronage on individual transit 124