The ENVIBASE-Project

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Traffic
Milan

Description of the Problem

Large concentrations of various human activities cause the emissions of significant amounts of pollutants. In particular, motor-vehicle traffic and the use of heating systems in winter are the main sources of air pollutants of inhabited areas.

As in many metropolitan areas, this is a major problem in the Lombardy Region, in particular because of the continuous increase in private vehicle traffic and the stagnation of public transport.

In 1991, people commuting in the metropolitan Aarea of Milan amounted to 1,040,000 compared with 795,000 in 1981, a 31 % increase. The size of this phenomenon is even more remarkable if one considers that in the same decade, the resident population of the area had a 3 % drop and the number of employees had only a 1 % increase. Concerning the transport means utilised, in 1991 out-of-town commuting generated a traffic of 538,000 cars (+69 %) compared with 318,000 in 1981.

Another significant parameter is constituted by the ratio of population to motor cars, which, in Italy, in the last few years, has stabilised at a value of about 1,8 inhabitants per car. In the metropolitan area of Milan, and in particular the city, this ratio has reached more extreme values (1.63 and 1.39 respectively). In the next few years, a levelling off can therefore be expected in the number of circulating vehicles.

According to an estimation of CORINAIR emissions inventory for 1990 in the metropolitan area of Milan, motor-vehicle traffic is the main CO source (about 80 %) and contributes, together with some industrial sources, to about half of NOx and, to a large extent, to VOC emissions. Within this frame, the traffic and pollution emergency must be faced in a more effective manner, in particular with new town-planning, traffic and transport joint policies, and air purification plans. Adopting and implementing "Town Traffic Plans" (TTP), which have been provided for the communities having a population of over 30,000, is often essential.

The main tools available for the control and the reduction of the effects of traffic pollution in Lombardy include:

Furthermore, a number of specific "technological" provisions have been devised to reduce emissions both at the regional and national levels, including in particular:

Data Sources

For the measurement of photochemical pollutants (NOx, O3), Italian norms provide the articulation of air pollution monitoring posts into four different classes depending on the type of localisation: A class, localised in areas that are not directly concerned with town emissions sources (parks, malls); B class, localised in high population density areas; C class, localised in high traffic areas; and D class, localised in outskirts or suburban areas.

In the Milan area, the number of posts of this type has increased, starting at the end of the 1980s, to represent now about half of the thirty-five posts included in the province area.

In order to monitor photochemical pollutants better, the number of D posts has also been increased in the two last years, especially in areas far from the direct sources of precursors. In addition, measurements with mobile laboratories are performed throughout the province territory.

The main sources of traffic data are:

Concerning traffic, both ANAS (Trunk Roads Management Company) and the Provinces (provincial roads), as well as the companies that manage motorway networks, carry out regular surveys of traffic flows and the composition of circulating vehicle fleet. For the Milan metropolitan area, ATM (Transport Public Utility) and the Milan municipality perform regular checks on the modalities and reasons of movement. The different municipalities of the metropolitan area carry out surveys on traffic flows within the frame of traffic planning.

Methods

The structure of the mathematical model system utilised to study vehicle-related air pollution is basically made up by three models:

The first model concerns the number of circulating vehicles and their travelling speed along the main arteries belonging to a road network.

The distribution of traffic flows ensuing from the application of an assignment model or, where it is unavailable, from the analysis of the assessments obtained by the measurement campaigns in the study area is the main entry parameter for the second model, which allows one to calculate the amount of pollutant emissions produced by the traffic of vehicles circulating along one single road or a whole road network.

EMITR emissions model, developed by PMIP - Milan Province, and applied to different study cases, utilises the emissions factors indicated by the CORINAIR - COPERT methodology. This methodology provides estimate algorithms of emissions factors as a function of the mean travelling speeds and driving types (town, out-of-town, and motorway cycle). Emissions factors are specified for some pollutants such as carbon dioxide (CO), nitrogen oxides (NOx), volatile organic compounds (COV), suspended particles (PTS), and sulphur oxides (SOx). Vehicles are articulated based on the type of fuel (petrol, diesel oil, LPG), the type of vehicle, and the application of EEC norms in the registration year.

Lastly, the dispersion model supplies the concentrations at which the emitted substances are present in the air by the effect of wind transportation and turbulent diffusion processes.

Results

Measurement campaigns and the related models required to draw up Town Traffic Plans and Mobility Plans, or the realisation of local emissions surveys, have been started in several municipalities of the Lombardy Region. In particular, for the Milan area, the available results include traffic emissions calculated for the town of Milan (20 x 20 km² grid, 1 km resolution), calculated on an hourly basis for average monthly days.

For the Milan metropolitan area, mean hourly emissions are available for an average monthly day calculated within the frame of the Road System Plan evaluation of the Milan province. Traffic flows have been calculated from the traffic assignment model of Centro Studi PIM, which takes into consideration more than 2.550 spans for a total of millions of kilometres/day, comprising the main spans of the Milan province. In both cases, emissions have been calculated by PMIP - Milan Province using the EMITR emissions model. This analysis was carried out within the frame of the pilot application of the ENVIBASE project.

The attached figure shows an example of NOx emissions distribution calculated on a 70 x 60 km² grid with 1 km resolution. In addition, the effects of vehicle-related air pollutant emissions following the adoption of some provisions included in the Mobility Plan of the Milan municipality in 1996 have also been calculated for the Milan area. For this purpose, the present emissions and the emissions expected for 2001 and 2006 respectively have been calculated considering the evolution of vehicle emissions factors. The extrapolations obtained show in general a reduction in traffic emissions. The renewal of the fleet to the advantage of the introduction of reduced emissions factors should allow one to obtain different amounts of reduction depending on the pollutants. The results show that the highest reduction will concern carbon monoxide -- up to 40-50 % -- within ten years. The Mobility Plan of Milan will undoubtedly contribute to this, with additional reductions of 5 to 15 %, depending on the pollutants. The emissions of nitrogen oxides and volatile organic compounds do not show the same evolution line, or at least they do not show a sharp reduction. One may therefore conclude that substantial reductions should be obtained by planning interventions in several directions, namely in the management of mobility with co-ordination and synergy between the plans on different territory scales (Town Planning Plans and Mobility Plans), paying special attention to the setting up of functions that can strongly attract or generate traffic, the development of public transport and the restriction of private vehicle mobility, the protection of public means, and lastly the regular control of vehicles, possibly extended to other pollutants besides carbon monoxide.

Results Analysis and evaluation methods Data
inventory maps / cadastral register Complex summarising / interpolation maps reference area / resolution / scale analogical / digital result calculation steps and spatial depiction main parameter Other necessary data Temporal distribution of data collection survey unit scale
Traffic volume   Province of Milan (2,400 km roads) Analog map and digital map E.I.S. Province of Milan - Centro Studi PIM Traffic Assignment Model - TRIPS
32 types of road spans articulated into three road classes:
- highways
- secondary highways
- town roads
Traffic volume (peak hours)   Data origin/ destination (O/D)
I.S.T.A.T. 1991 updated as at 1955. 30 surveys carried out on ordinary roads in two work-days in two morning peak hours, and 11 surveys carried out at the motorway barriers of Milan on 24 hours of 2 work-days.
5,144 road stretches
312 zones
    Municipality of Milan and hinterland Analog map and digital map E.I.S.
A.T.M. (Milan Transport Public utility)
A.T.M.Traffic Assignment Model - The roadways is shown by a diagram wherein reference is made to the geometric and travel characteristics of the individual itineraries.     O/D (1994) matrix elaborated by A.T.M., updated every year based on computations by town traffic wardens. Recently, a new O/D (1995) matrix. 3,500 spans
660 zones
  Traffic-related air polluting emissions Province of Milan Analog map and digital map E.I.S.
P.M.I.P./ Province of Milan
EMITRE MODEL INPUT DATA: out-of-town road layout, peak hour traffic flows, fleet composition (cars, trucks, motorcycles, buses) and age distribution
CORINAIR-COPERT (emission factors-temperature)
SO2, CO2, Ox, VOC, PTS      
Analysis of road network and traffic volumes
- vehicle/km
- vehicle/
hours
- km of congested network
- comparison of traffic volumes with alternative planning scenarios
  Lombardy Region
Regional or provincial areas or local areas of particular interest (e.g., Malpensa Airport).
Different scale maps using a Geographic Information System The whole analysis is based on the use of a Geographic Information System: the main parameters are calculated on the basis of the data (i.e. capacity) or by intersecting road network with other ones, e.g. urbanisation cover and administrative boundaries.
Trip, a software for traffic assignment, distributes on the network traffic volumes calculated and calibrated based on regular surveys.
- traffic volume (average day)
- speed
- capacity
stretches representing road spans
- functional and geometric characteristics used
(width, no. at carriageways)
- continuous updating of road characteristics
- 14 prefixed days in a year measurements of traffic volumes
all regional road system
1:10000 scale
Traffic emission Traffic emission-related air pollution Lombardy Region Region E.I.S.
AURORA
NEBULA
Time and space disaggregation methods by Lombardy Region of CORINAIR ’90 emission data. SO2, CO2, NOx, VOC, PTS      

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