Spatial distribution of emissions to air - the SPREAD model

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and Environmental Planning slightly modified by adding a small number
of urban areas from a zone map from AIS in 1999 (Levin, 2009).
ADT of roads in urban areas is determined for each grid cell based on the
assumption that roadwork is distributed in the same proportion as the
area of urban and rural areas within each grid cell. This approach is chosen
over an analysis of the entire road network since it is far less labour
intensive and since it is assumed that the benefit to the total uncertainty
will be insignificant, the purpose (modelling of air quality) taken into account.
The same approach is applied for roads in rural areas. Figure 3.3
shows the traffic load for passenger cars on the Danish road network aggregated
on the 1x1 km grid.
Figure 3.3 Traffic load for passenger cars including two-wheelers on the Danish road network according to the National
Road and Traffic Database (NRTD).
A set of distribution keys based on ADT for the nine categories is set up
in a Microsoft Access database model for subsequent data processing. A
number of checks are run to test the model e.g. sum check of the total
ADT. Further, a visual validation is made in GIS to ensure that all grid
cells with an associated ADT are located on land or at the road network
including piers and bridges. A grid net covering a square around the
Danish economic zone is applied to ensure that cells outside the border
of the Danish area of land is not lost during data processing.
The Danish emission inventory system includes mileage comparable to
ADT in NRTD. Deviations between ADT and mileage are expected as
they are based on different input data and methodology. The deviations
owe to differences in assumptions of the total ADT and to difference in
the estimation of traffic loads for the road and vehicle categories. A comparison
of ADT and mileage is made to identify and quantify the devia-