2018-165 Transportation Plan - Laserfiche WebLink

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Forecasts Forecast Process The traffic volume forecasts are based upon projected changes in land use, changes in interaction with the area outside of the model, changes in travel behavior, and changes in the transportation system. Typically, as the number of households and jobs increase, the traffic will increase as well. The calibration can be looked at as building and checking the "rules" for traffic generation, distribution, and assignment in the Kittitas County area. Then, as changes are made these same "rules" are used to project the change in traffic volumes and resulting changes in congestion, travel time, and emissions. The forecast process requires the projected number of housing units, projected number of employees by land use classification, number of acres of agricultural land, etc. It also requires a forecast of interaction with the area outside of the models. Information is needed to project the trips that enter and leave the model area. Finally, any planned transportation improvement projects should be included to properly assess the future operation of the transportation system. Each of these items is discussed. Land Use Forecasts Several sources were used to compile the forecast land use scenario. Previous work on forecast land use had been done by Studio Cascade, a land use planning consulting firm. Studio Cascade examined land use in Ellensburg during 2005 and compiled a forecast scenario for Ellensburg zones. Kittitas County also supplied PTV America, Inc. with a forecast scenario using growth factors with three ranges. It was decided to use a combination of these sources of forecast information to produce a detailed and more accurate land use forecast. The general methodology included using forecast data from Studio Cascade for all Ellensburg zones while using Kittitas County forecast data for all other zones with some exceptions. External growth was similarly adjusted. Typically external growth is based upon trends analysis. The area surrounding a model study area is usually not experiencing congestion or volume-to-capacity problems. It is usually sufficient to analyze historical trends based upon traffic counts and extrapolate these trends into the future. Caution should be used if any of the trend extrapolation pushes the traffic volume on any external close to its capacity. WSDOT ATR count data was used from 1997 to 2007 to establish trends. The growth rates were between 2.5% per year (for 1-90) to less than Kittitas County, Washington Trans portation Model -May 2009 Page45