Traffic Forecasting Accuracy Assessment Research (2020) / Chapter Skim
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III-F-1 Literature Review A P P E N D I X F Contents III-F-2 1 Introduction III-F-2 2 A History of Forecast Evaluations III-F-5 3 Existing Systematic Review Programs III-F-6 4 Summary of Existing Outcomes III-F-9 5 Methods of Evaluation III-F-14 6 Identified Problems with Forecast Accuracy III-F-14 7 Gaps in Knowledge III-F-16 References
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III-F-2 Traffic Forecasting Accuracy Assessment Research 1 Introduction The current assessment of traffic forecasting accuracy in NCHRP Project 08-110 builds upon past efforts. This document summarizes those efforts, and what can be learned from them for the current study.
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Appendix F: Literature Review III-F-3 The number of forecasting accuracy assessments have increased since the year 2000. Bent Flyvbjerg released his seminal work on forecasts for multiple modes (Flyvbjerg, Holm, and Buhl 2005)
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III-F-4 Traffic Forecasting Accuracy Assessment Research From 2002–2005, Standard & Poor's publicly released annual reports on the accuracy of toll road, bridge, and tunnel projects worldwide. The 2005 report (Robert Bain and Polakovic 2005)
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Appendix F: Literature Review III-F-5 The research also investigated three commonly held beliefs regarding forecasting accuracy: More recent projects are more accurate than older ones (i.e., forecasts are getting more accurate as tools become more advanced) , Forecasts are more accurate in later stages of project development than in earlier stages (i.e., the more that is known about the details of a project, the more accurate the forecast of demand)
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III-F-6 Traffic Forecasting Accuracy Assessment Research those differences and highlights lessons learned that would inform FTA or other project sponsors about how methodologies or circumstances helped or hindered the predictions. The FTA's New Starts program allows project sponsors to enumerate the uncertainties inherent in their travel forecasts and provide information on how those uncertainties may impact the project forecast.
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Appendix F: Literature Review III-F-7 information considered. Table III-F-2 shows the studies included, and Table III-F-3 shows a summary of the results included.
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III-F-8 Traffic Forecasting Accuracy Assessment Research The main finding from this paper is that the observed inaccuracy of forecasts varies based on the type of project: For rail projects, the mean inaccuracy is negative, meaning that actual demand is less than the demand that was predicted. The general range is that actual demand is 16%–44% less than forecast demand.
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Appendix F: Literature Review III-F-9 5 Methods of Evaluation The next question of particular relevance to this study is how to go about assessing forecast accuracy. For this question, we consider a selection of studies as summarized in Table III-F-4.
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Table III-F-4. Summary of select studies and methods.
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Paper Title Research Data Analysis Procedure Results Suggestions/Sources of Error Bain (2011) On the reasonableness of traffic forecasts Survey of forecasters Surveyed forecasters to identify how accurate they expect forecasts to be Expected accuracy for an existing road is +/-15% 5 years out, +/-32.5% 20 years out.
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Table III-F-4 (Continued)
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Appendix F: Literature Review III-F-13 The null hypothesis is that the forecasts are unbiased, and in that case the estimated value of will be 0 and of will be 1. Odeck and Welde (2017)
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III-F-14 Traffic Forecasting Accuracy Assessment Research 6 Identified Problems with Forecast Accuracy A component of the deep dives will be an effort to assess the sources of forecast error. A number of authors have proposed a range of hypotheses for what those sources may be.
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Paper Employment GDP Recession / Econ Condition Trip Gen / Travel Characteristics Land Use Population Projection Housing Prediction Car Ownership Fuel Price Fuel Efficiency Time Savings Location Time of Operation Toll Road Capacity Length of Road Cash Payment / Value of Time Ramp Up Period Tolling Culture Time-ofday Traffic calculations Forecast Duration Odeck and Welde 2017 Gomez, Vassallo, and Herraiz 2016 Y Y Y Li and Hensher 2010 Y Y Y Y Flyvbjerg et al. 2006 Y Y Bain 2011 Y Y Y Y Y Y Y Bain 2009 European Court of Auditors 2013 Chatterjee et al.
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III-F-16 Traffic Forecasting Accuracy Assessment Research References Anam, S., J
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Appendix F: Literature Review III-F-17 Hartgen, D
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