traditional distinction is between urban roads,
rural roads, and motorways. Vehicle operation is
therefore only taken into account at a very rudimentary level. However, they are generally the
only way of estimating emissions of unregulated
pollutants, for which there is often insufficient
information to define a more detailed relationship
with vehicle operation.
Average-speed models are based upon the principle that the emission factor varies according to
the average speed during a trip. The general process of model development is shown in Fig. 8.
Firstly, vehicle operation in the real world is measured using on-board instruments, with the vehicles being driven under a wide range of road and
traffic conditions. The numerous resulting driving
patterns are then condensed, using statistical
methods, into a much smaller number of representative driving cycles which can be used to test
vehicles in the laboratory. The results from the
laboratory tests on vehicles in the same category
(e.g., small petrol cars complying with the Euro
4 legislation) are then plotted as a function of
average speed, and a regression curve is fitted to
the date to give an emission function. Given that
exhaust emissions are inherently variable, there is
usually a considerable amount of scatter in the
emission data.
Average-speed models are widely used in
emission inventories and local air pollution
models. In Europe, the most widely used example
is COPERT [33]. A number of factors have contributed to their popularity. The modelling
approach is one of the oldest, it is comparatively
easy to use, several models are available free of
charge, and there is a reasonably close correspondence between the required inputs and the data
available to users. However, trips having very
Real-world driving patterns
Laboratory measurements
Record of vehicle
operation via
OBD, GPS, etc.
Driving cycles
Emission function
ARTEMIS Urban, part 2
NOx (g/km)
Laboratory measurements
Emission function
0.6
0.5
0.4
0.3
0.2
0.1
0
0
4 0
8 0
Speed (km/h)
120
160
ARTEMIS Rural, part 4
200
180
160
140
120
100
Time (s)
80
60
40
20
0
180
160
140
120
100
Time (s)
80
60
40
20
0
0
20
40
60
80
0
40
120
80
Speed (km/h)
Speed (km/h)
Air Quality, Surface Transportation Impacts on,
Fig. 8 Process of development for average-speed models.
(Photographs reproduced by kind permission of Alistair
Smith, Tim Barlow of TRL in the UK, and TNO Automotive in the Netherlands)
58
Air Quality, Surface Transportation Impacts on
rural roads, and motorways. Vehicle operation is
therefore only taken into account at a very rudimentary level. However, they are generally the
only way of estimating emissions of unregulated
pollutants, for which there is often insufficient
information to define a more detailed relationship
with vehicle operation.
Average-speed models are based upon the principle that the emission factor varies according to
the average speed during a trip. The general process of model development is shown in Fig. 8.
Firstly, vehicle operation in the real world is measured using on-board instruments, with the vehicles being driven under a wide range of road and
traffic conditions. The numerous resulting driving
patterns are then condensed, using statistical
methods, into a much smaller number of representative driving cycles which can be used to test
vehicles in the laboratory. The results from the
laboratory tests on vehicles in the same category
(e.g., small petrol cars complying with the Euro
4 legislation) are then plotted as a function of
average speed, and a regression curve is fitted to
the date to give an emission function. Given that
exhaust emissions are inherently variable, there is
usually a considerable amount of scatter in the
emission data.
Average-speed models are widely used in
emission inventories and local air pollution
models. In Europe, the most widely used example
is COPERT [33]. A number of factors have contributed to their popularity. The modelling
approach is one of the oldest, it is comparatively
easy to use, several models are available free of
charge, and there is a reasonably close correspondence between the required inputs and the data
available to users. However, trips having very
Real-world driving patterns
Laboratory measurements
Record of vehicle
operation via
OBD, GPS, etc.
Driving cycles
Emission function
ARTEMIS Urban, part 2
NOx (g/km)
Laboratory measurements
Emission function
0.6
0.5
0.4
0.3
0.2
0.1
0
0
4 0
8 0
Speed (km/h)
120
160
ARTEMIS Rural, part 4
200
180
160
140
120
100
Time (s)
80
60
40
20
0
180
160
140
120
100
Time (s)
80
60
40
20
0
0
20
40
60
80
0
40
120
80
Speed (km/h)
Speed (km/h)
Air Quality, Surface Transportation Impacts on,
Fig. 8 Process of development for average-speed models.
(Photographs reproduced by kind permission of Alistair
Smith, Tim Barlow of TRL in the UK, and TNO Automotive in the Netherlands)
58
Air Quality, Surface Transportation Impacts on