Root-mean-square error (%RMSE). This describes the average model error in relation to the average counted volume and represents the spread from the regression line. Values under 35% are desired. The updated North Bend model has a value of 28%.
Allowable errors. A federal research study (National Academy of Sciences - Transportation Research Board, National Cooperative Highway Research Project #255, Highway Traffic Data for Urbanized Area Project Planning and Design, 1982). provides a well-known formula for allowable differences between model volumes and counts. The formula permits higher percentage errors on low-volume roads and lower percentage errors on high-volume roads. Obviously, the consequences of forecasting error will be greater on major roads. A high percentage of links with modeled volumes within this allowable range is obviously desirable, but no absolute standard is provided. It is recommended that 75% of links classified as Principal Arterial and above are within these limits. The updated North Bend model has 92% of ALL counted links within these limits. These statistics show that the updated North Bend, WA Traffic Model is calibrated to an acceptable level to be used for forecasts.
MODEL RUN PROCEDURES The PTV Vision VISUM version (.ver) files are supplied to the City for future use. All filter and other files are included with these files. There are three model run parameter (.par) files to be used for running the model. North Bend Model Run 06082011.par – This file should be loaded for re-running base year calibration or validation if the network or land use is changed. North Bend Forecast Run 10072011.par – This file should be loaded for running additional forecast alternatives if the network or land use is changed. North Bend Intersection LOS 06082011.par – This file is loaded and used to run intersection LOS after one of the two procedures have been run. This will result in an excel spreadsheet being created that contains details on each intersection analyzed and a summary sheet showing the average and worst turn LOS.
Appendix D
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