Traffic Forecasting Accuracy Assessment Research (2020) / Chapter Skim
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I-46 Reporting Accuracy Results The project team recommends that agencies involved in producing traffic forecasts periodically report the accuracy of those forecasts relative to observed data. It is recommended that this reporting include three components: 1.
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Reporting Accuracy Results I-47 4.2 Summary Reports Several metrics are used to report accuracy results. A popular metric used to determine the accuracy of traffic forecasts is the half-a-lane criterion.
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I-48 Traffic Forecasting Accuracy Assessment Research team recommends showing the entire distribution of the selected metric(s) in a frequency chart because using only the average or mean error rates can mask important fluctuations.
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Reporting Accuracy Results I-49 4.3 Updating Quantile Regression Models As discussed in Part I, Chapter 2, quantile regression models can be used to estimate the uncertainty window around a forecast. A set of default models is provided with this guidebook; however, if an agency has collected data on traffic forecast accuracy, the quantile regression models can be re-estimated using the local data.
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I-50 Traffic Forecasting Accuracy Assessment Research In Equation I-7, αq is an estimated constant and βq is an estimated slope; X1,i through XN,i are descriptive variables associated with Project i, and γq,1 through γq,N are estimated model coefficients associated with those descriptive variables and those quantiles. Each variable is multiplied by ŷi, which makes the effect of that variable scale with the forecast volume (i.e., change the slope of the line)
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Reporting Accuracy Results I-51 forecasts that are highly accurate or inaccurate. The next section in this chapter describes scripts that are provided to compile forecast accuracy data in a format suitable for quantile regression estimation.
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I-52 Traffic Forecasting Accuracy Assessment Research regression models where the actual value is the dependent variable and the forecast value is the descriptive variable. An estimate_quantiles script is provided to estimate a basic model with just this one variable.
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Reporting Accuracy Results I-53 Elasticities measure the change in the traffic forecast given a known change in an input or assumption to the forecast. Elasticities are usually expressed as ratios.
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