Post-Construction Evaluation of Forecast Accuracy

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Nexus group (Pavithra Parthasarathi and David Levinson) recently completed a study for MnDOT on the
Post-Construction Evaluation of Forecast Accuracy. A version of this was recently presented at TRB.

The net is, in the Twin Cities, freeway traffic was underestimated while non-freeway traffic was overestimated. The reasons are many.

This research evaluates the accuracy of demand forecasts using a sample of recently-completed projects in Minnesota and identifies the factors influencing the inaccuracy in forecasts. The forecast traffic data for this study is drawn from Environmental Impact Statements (EIS), Transportation Analysis Reports (TAR) and other forecast reports produced by the Minnesota Department of Transportation (Mn/DOT) with a horizon forecast year of 2010 or earlier. The actual traffic data is compiled from the database of traffic counts maintained by the Office of Transportation Data and Analysis at Mn/DOT. Based on recent research on forecast accuracy, the inaccuracy of traffic forecasts is estimated as a ratio of the forecast traffic to the actual traffic. The estimation of forecast inaccuracy also involves a comparison of the socioeconomic and demographic assumptions, the assumed networks to the actual in-place networks and other travel behavior assumptions that went into generating the traffic forecasts against actual conditions. The analysis indicates a general trend of underestimation in roadway traffic forecasts with factors such as highway type, functional classification and direction playing an influencing role. Roadways with higher volumes and higher functional classifications such as freeways are subject to underestimation compared to lower volume roadways and lower functional classifications. The comparison of demographic forecasts shows a trend of overestimation while the comparison of travel behavior characteristics indicates a lack of incorporation of fundamental shifts and societal changes.

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Any forecasting which requires knowledge of unknowable social and economic variables is immediately flawed, in my opinion. I certainly respect the efforts of Mn/DOT to be preemptive, but I don't put much stock in it. It's like trying to predict the stock market, construction industry, or wars.

David Levinson

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This page contains a single entry by David Levinson published on February 17, 2009 3:14 PM.

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