Introduction
In 2001 the City of Venice, using
the technical support of ARPAV (the Environmental Regional Agency), conducted an estimate
of the atmospheric emissions from
road traffic.
The aim of the study was to identify the most polluted urban roads, so as to
implement better atmospheric pollution control policies by means of road traffic measures, as provided for by DM
163/99 (now partially repealed with adoption of the EU Air Quality Directives).
The analysis provided the following evaluation elements,
useful for planning actions on traffic and its components:
- definition
of higher emission potential vehicle typologies, for each pollutant (see the
average emission factors for vehicle category);
- identification
of the main vehicle class responsible for overall emissions
for each pollutant (see relative forms of the overall polluting emissions -Kgs
issued during peak
hours-);
- hierarchization
of the urban road network according to the emission density class;
- definition
of the higher-density
roads, in urban and extra-urban road systems
(critical roads);
- critical road hierarchization
for C6H6 and PM10 emissions, according to a “vulnerability
index”, taking into account residential density in the areas adjacent to the road, and therefore
the impact on the residential population, and
consequent “sensitive areas” identification.
Short description of the estimate
methodology
The estimate of
atmospheric pollutant emissions caused by road traffic was carried out using the COPERT III methodology (COmputer
Programme to calculate Emissions from Road Traffic, version III) proposed and
suggested by the European Environment Agency (EEA, 1999).
The methodology was developed from the concept that the
vehicle emission factor, or rather
the emitted polluting quantity, depends on a number of variables:
-
vehicle category (passenger vehicles, commercial light vehicles,
commercial heavy-duty
vehicles, motorcycles
and motor vehicles, buses)
-
fuel
type (gasoline, diesel oil, LPG);
-
registration
year (with reference to the European legislation on emissions reduction);
-
engine
displacement (for cars and two-wheel
vehicles) and overall weight (for commercial vehicles);
-
average
vehicle driving speed (in urban area, in rural areas, along highways or high-speed
roads);
-
average
vehicle speed;
-
fuel
consumption;
-
climatic situation (environmental temperature).
The methodology differentiates the overall emissions caused by road
vehicles, taking into account three major final
components:
1. combustion
emissions, divided into:
- hot emissions caused by vehicles with an
average running motor speed (temperature = 90°C ca.);
- cold over-emission caused by vehicles during the vehicle heating
stage;
2. evaporative emissions, only
for COV, from which those for C6H6 are derived divided
into:
- in
the daytime, from cold engine vehicles;
- hot
soak, from hot vehicles just turned off;
- running
losses, from in-gear
vehicles;
3. degraded hot emissions,
calculated from hot emissions multiplied by a degradation coefficient,
determined by vehicle age and average distance covered; this component
considers the catalytic converter
degradation (therefore the emissions increase due to catalytic vehicle ageing).
Database for the implementation of COPERT III
methodology
The original data for the reconstruction of the entire
municipal area vehicle traffic have been provided by the outputs of the traffic
model used by the
City of Venice, Land
Development and Mobility Department, Mobility Office.
The City of Venice Mobility Office uses the EMME/2 traffic
model (Transport
Planning Software: Modelling and Analysis Features, by INRO Consultants
Inc., Canada), a multimodal planning transport
system that supplies tools for transport
demand modelling, for transport
offer and their interactions (Origin/Destination matrix model).
Its main characteristic is the capacity to reach an
assignation in multimodal balance conditions, that is
simulating a real situation taking into account
all the existing territorial transport
services (public and private network, heavy-duty
commercial traffic, etc., up to 30 different transport
modalities).
The EMME/2 model uses the Origin/Destination matrix
traffic flows (matrix from the 1991 ISTAT General Survey) integrated and supplemented for measureless roads with data surveyed during specific research and the
knowledge of experts operating within the Mobility Office.
At the end of COPERT III methodology implementation,
we have the following information:
- the road
network design (983 roads, totalling about 420 Km) representing the urban and
extra-urban network of roads (see map 3);
- “oriented
(or “directional”) design” characteristics, that is the oriented roads set
(characterized by knot couples with metric coordinates “x,y” called “initial knot” and “final knot”), representing the two
directions or a single one-way
direction;
- rush
hour traffic flows (7.30-8.30
a.m.) divided into: cars, motorcycles,
vans (disaggregated from the “light” class model) and heavy duty (“heavy-duty”
model), see
map 4 and map 5;
- flows
subdivision percentage of the “Heavy” category into: “Heavies” and “Buses”;
- flows
attribution percentage of the “Motorcycle” and “Buses” along some traffic flow
roads;
- flows
attribution percentage of the “Heavies” category along high-density
traffic roads;
- flows
attribution percentage of the “Buses”
category along high-density
traffic roads;
- average speed per road, not differentiated for all
categories.
The aim of the traffic data analysis has been the
creation of a traffic database suitable to the COPERT III methodology
implementation for the vehicle traffic emissions in the City of Venice urban
area.
Such methodology requires as an input
a lot of information, such as the definition of the vehicles mileage concept,
defined as the relationship between the number of vehicles along a road and its
length.
The vehicular traffic polluting emissions have been
calculated as a relationship between the different vehicle
mileages and the specific emission factors (g/Km), themselves defined as average vehicle emissions
covering one Km.
The results of the traffic
data analysis have been the following:
- reference
scenario identification: rush hour 7.30-8.30
a.m.;
- subdivision
of all links of the road design into the two directions;
- mileage
characterization for each vehicle category;
- traffic flux characterization, calculated taking
into account the mileages, for each
link and vehicle category: motorcycles, cars, light vehicles, heavy-duty
vehicles, buses.
During morning rush hour, about
400,000 Km
are covered by all vehicles along the design urban and extra-urban network.
Registered car fleet analysis
The registered car fleet is used to assign all vehicles
circulating in the urban area to the 105 emission categories defined by the
COPERT III methodology.
The registered car fleet data supplied by ACI (Automobile Club Italia) at provincial
level (1999) have been considered in relation to the types of vehicles circulating in the urban
territory of Venice.
The ACI registered data does not include motorcycles
(because they pertain to the Provincial Road Traffic Authority). Hence
data has
been taken from the ANCMA Data Base (National
Cycle Motorcycle Accessories Association).
The entire registered vehicle number in the Venice Province in 1999
is 489,368,
with the following subdivisions into
vehicle categories:
-
mopeds
and motorcycles 9%:
-
cars
83%;
-
commercial
light vehicles 5.6%;
-
commercial
heavy-duty
vehicles and trucks 2%;
-
buses
0.4%.
In 1999 the overall situation of the Province of Venice car
fleet was the following:
-
52% non-catalytic
vehicles (conventional);
-
48% catalytic vehicles (non-conventional).
Results of the analysis of the emissions produced
by traffic in the Mestre urban area
Firstly the average emission factors have been
calculated for the 5 vehicle categories of mopeds
and motorcycles, cars, commercial light vehicles, commercial heavy-duty
vehicles and trucks and buses.
By average
emission factor we mean the polluting amount emitted by
a single considered category vehicle covering one Km.
Such average value can be obtained by dividing
the overall emission of the vehicle category in
question (added on the roads) into the overall transit (added on
the roads) of the same category. It therefore represents the emission factor
(g/Km) of an “average vehicle” of such a category, along a trail under
average speed conditions.
As issuing components, the
hot and cold-over emissions and the evaporative running-type emissions have been considered (also the degraded
ones).
The emissions were computed for the entire Mestre and Marghera network and were drawn up during the rush hour (corresponding to the period 7:30-8:30), for the first six pollutants: NOX, CO, VOC, C6H6,
PM10 and TSP. Data have been expressed in (kg/rush hour).
The emission contribution of the
different vehicle categories, in comparison with the rush hour overall
emissions, has underlined the emissions of:
- C6H6 is almost exclusively due to cars (77%)
and motorcycles (19%);
- CO presents similar characteristics (car 77% and motorcycles 13%);
- NOX are produced by commercial heavy duty vehicles and
trucks (51%), cars (32%) and buses (12%);
- VOC are produced by: cars (59%), commercial heavy duty vehicles
and trucks (23%) and motorcycles (13%);
- Total Suspended Particle (TSP) and PM10 are due to
commercial heavy duty vehicles (68%), commercial light vehicles (12.5%), cars
(10%) and buses (9.5%), while motorcycles have no PM10 emissions.
-
It is important to remember that the COPERT III estimates only the TSP
deriving from diesel vehicles. Given the health importance of PM10, previous
research has shown that about 96% of particulate matter produced by vehicular
traffic is PM10.
The evaporative emission from cold-engine
vehicles has also been calculated for VOC and C6H6
. Such an estimate
has been carried out only for a 24h scenario.
The emission pressure evaluation
of urban roads in comparison with extra-urban has underlined that:
- for CO, C6H6 and VOC, the weight of the
urban factor prevails over extra-urban;
- for NOX, TSP and PM10 the
weight of the urban factor prevails less in comparison with the extra-urban
one.
Sensitive areas identification
Once identified, the
urban links characterized by higher linear emissions (g/km), were compared with the
emissions (see
map 6, map 7,
map 8,
map 9,
map 10
and map
11) of the
geo-referenced population density,
expressed in (inh./ha). This
operation was
synthesized in a “vulnerability
index” of population residing in areas characterized by the highest
traffic intensity roads, considered as
representative of a 50 m range of action from the examined road.
The index is expressed as the relationship between emission density and population
density (population residing in the survey sections crossed by the examined
road (inh./ha * g/Km). The “sensitive areas” thus identified were
successively put in a hierarchy taking
into account
both traffic pollution (approximated to
the emission density expressed in g/Km) and the presence of population
(approximated to the residence density expressed in in h./ha).
The use of the population
density represents a limit to the index calculation: where the density is
equal to zero, likewise the vulnerability is equal to zero.
To overcome the lack of homogeneity in some survey
sections (very wide and with a low resident population, or on the contrary, a small
area and high population concentration) average and maximum residential
densities have been considered (between all the interested sections), and
therefore the corresponding
medium and maximum vulnerability indexes have been derived for the two
parameters posing the greatest health
risk : C6H6 (see map 12)
and PM10 (see map 13).
Full
text report 2001: full text report (in Italian language), see
Appendix 1 (APPENDIX 1: Emission estimate
by vehicle traffic with implementation of the COPERT III
methodology in the City of Venice).
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