When you have a fleet
of vehicles in your town (or area) you must find information that is important
for your Air Quality Management System like emission database and dispersion
modelling software etc. To calculate emission on an annual basis you must have
information about the distribution of the vehicles, traffic network and
emission factors etc. When using dispersion calculation models you also must
have dynamic data information concerning monthly and daily variation of the
traffic (divided in the type of vehicles).
The vehicle exhaust
emissions may be influenced in two principal ways: by changing the composition
of the traffic or by changing the way in which the vehicles are operated. To
have that kind of information you also must have traffic data in real time and
historical.
To obtain real time
traffic data you must have a well defined data protocol. The protocol will be
used initially to exchange traffic measurement data. Traffic measurement data
can be both static and dynamic. Static data, e.g. the names
of locations which do not change frequently. Dynamic data, e.g.
measurements from a location, which changes frequently, sometimes several times
a minute. Because of this the data is made available in two ways. Static data
is returned on request. Dynamic data is returned on request or subscribed to.
If subscribed to, the data will be delivered to the application as soon as it
is changed.
Location data consists
of static information regarding measurement locations etc. This includes
information on the identity of the location, the coordinates of the location,
possible sampling intervals, what parameters are measured, number of lanes etc.
A location is the name for a geographical point where traffic measurement is
possible.
Traffic measurement
data consists of information on measurement location, sampling interval,
traffic flow, traffic speed etc.
On the other side, the
emission results from EU tests are not always representative for emission
behaviour of the modern vehicles in real world driving conditions: measurements
have pointed out that new technologies can have a different
emission behaviour in real traffic compared to European tests resulting in
higher emissions.
In particular Heavy
Duty vehicles are the major polluters (especially for NOx
and PM) in cities and have a high emission reduction potential as demonstrated
in the London Low Emission Zone feasibility study.
Buses of public
transport companies have a special role since transport companies can perform a
role model function regarding clean transport: besides new diesel fuelled
vehicles (Euro 4 starting from 2005), vehicles on alternative fuels and
retrofitted vehicles can contribute to a clean city.
The integration between
on-board measurements and information on traffic condition should be both used
for the evaluation of different situations: data provided by the measurement
campaigns will be the scientific base for the evaluation of pollution volumes
and will provide quantitative data input to the air quality modelling and
impact monitoring.
Representative routes
may be chosen in the city area and defined as a representative driving cycle.
The most representative
vehicles may be evaluated based on measurements performed driving this cycle:
this will make it also possible to compare different technologies in similar
conditions and real traffic.
During operation emissions (CO2,
CO, NOx, THC, PM), fuel
consumption and engine parameters (speed, engine speed, lambda) have to be
measured.
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