Errors In Model Predictions Of NOx Traffic
Emissions At Road Level –
Impacts Of Input Data Quality
Author(s)
R. Smit
Abstract
This study investigates the effects of three important input variables on the
prediction accuracy of average speed emission models. These variables are
average speed, basic traffic composition (proportion of heavy-duty vehicles) and
model choice (COPERT, QGEPA). Sensitivity analysis (conditional NRSA) is
used to determine to what extent the possible range in these input variables
influences model outcomes (i.e. NOx emissions for road links), and hence
accuracy. It is shown that maximum errors can be large (up to a factor of about
3.5). Moreover, they are a function of the level of congestion with errors
generally increasing with the level of congestion. Traffic composition is shown
to most strongly affect NOx emissions (29-241%), followed by average speed (2-
168%) and model choice (0-177%). The results were similar for arterial roads
and freeways. These results can be used to provide direction to the collection of
model input data, further model development and model application. The
external errors found in this study appear to be of the same order of magnitude as
internal errors that have been reported from (partial) road validation studies. This
implies that in terms of further improvements of traffic emission modeling, focus
should be on both the quality of input data (application) and the quality of the
actual emission models (model development). Given the relevance of these
results, it would be worthwhile to extend and refine this work by including other
air pollutant and greenhouse gas emissions, and to use more complex traffic and
emission models.
Keywords: accuracy, error, road traffic emission, modeling, sensitivity analysis,
NOx, congestion.
Keywords
accuracy, error, road traffic emission, modeling, sensitivity analysis,
NOx, congestion.
Related Book
Other papers in this volume
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