The ENVIBASE-Project

Documentation / Online Handbook

Traffic

Rome

Description of the Problem

As was stated in the chapter on air quality, traffic is responsible for about 85 % of total air pollution in Rome, a marginal share of which consists in pollution that is a result of electric power generation (only 5.5 % of transportation demand makes use of electric power-operated public transportation, such as railway, tramway, subway).

The transportation demand has been estimated, according to the most recent calculations, to equal about 5,873 million trips in the surveyed day. Of such a total amount of trips, 20.6 % are pedestrian trips, 25.7 % are public transportation trips, including 0.4 % using taxis, and 53.7 % are trips using private transportation modes, mostly private cars and motorbikes.

From the point of view of air pollution, the private transportation mode has a high impact per user, considering that most of the cars, as well as the motorbikes, transport a single user (86 % of cars). The car fleet is rapidly changing, from cars operated with normal fuel to cars operated with green fuel. Concerning the public transportation mode, most of the trips make use of the bus, which is fuel operated (77 % of public transportation), while 22 % of public transportation users are transported by electric power-operated vehicles. The remaining 1 % of public transportation consists of taxi trips.

In the following sections, we will summarise the data required and the methods applied to support the decision makers in such programmes aimed at reducing traffic-induced air pollution. At the same time, we will make a brief reference to the emergency provisions, in case of peaks in the level of air pollution, and to the data and methods used to monitor the traffic-induced air pollution in order to detect such peaks in the concentration of polluting agents.

The emergency provisions are ruled by the following regulations:

DPR 24 May 1988, n.203 (regulation issued by the President of the Italian Republic), about the application of the EU Directives n. 80/779, 82/884, 84/360 and 85/203, concerning rules on the matter of air quality related to specific polluting agents;
DM 20 May 1991 (regulation issued by the Ministry of the Environment), about the criteria to be applied in the Regional Plans for the preservation and improvement of air quality;
DM 12 November 1992, about general criteria to prevent the air pollution in large urban areas and to improve the air quality;
DM 15 April 1994, about technical rules on the matter of air pollution levels leading to the release of attention and alarm warnings related to air pollution in urban areas.

The last regulation particularly establishes the levels considered as thresholds which, if exceeded in a group of air monitoring stations, cause the development of the actions implied in the attention and alarm warnings. A group of air monitoring stations means a share of them, from the total, also considering their type, according to the types explained in the chapter on air quality. The attention warning consists, with slightly different procedures among the different polluting agents (carbon oxide, nitrogen dioxide, ozone), in an increase of information to citizens and, if the pollution levels persist for more than eight hours or if higher thresholds are passed, in the release of an alarm warning, which means the prohibition of using cars not equipped with catalytic converters within the perimeter of the inner city.

If we consider the number of attention and alarm warnings as an indicator of air quality, we can conclude that in the years from 1993 to 1996 there was a substantial improvement. Attention warnings dropped from 91 in 1993 to 26 in 1996, while alarm warnings and car traffic blocks (for non-catalytic cars) dropped from 9 in 1993 to 3 in 1996.

Concerning the structural provisions which depend on the local government, they can be divided into the following three groups:

provisions for impoving the efficiency of the street network, by establishing differentiated regulations for the different parts of the city and the different types of arcs of the street network;
provisions for developing the public transportation network;
planning of the street network, with the integration of new arteries.

All these types of provisions require a complex knowledge of the transportation sector, both on the demand and on the supply side. Mainly two methodological instruments, and the related database, were then developed for such purposes:

the classification of the arcs of the street network, according to their suitability for the transportation functions, within the peripheric highway (including an area of about 365 km²);
the implementation of the transportation system simulation model EMME/2 (Equilibre Multimodal, Multimodal Equilibrium, release 2).

On the side of the monitoring and forecasting of air quality, more sophisticated instruments were experimented with in order to have an increased capacity to predict the peaks and the evolution of pollution phenomena and then to apply more efficient emergency provisions.

All these methodological instruments, and the related database, will be analysed hereafter. Lastly, the effect of this improved knowledge will be seen in the results of the support given to the decision makers in the definition of provisions to decrease the traffic-induced air pollution.

Data Sources

In the implementation of the above-mentioned transportation planning instruments, the following data were available:

database of the street network, described by elements such as arcs, nodes, intersections with constraints; the information associated with such elements are: length, available transportation modes, number of lanes, type of flow function (speed/flow-conditions functions) for each arc, some characteristics with influence on the traffic flow, turn penalties at the intersections, etc.;
database of the railway and subway network;
databases of the vehicle fleet (bus, tram, subway, and railway truck) and of the public transportation lines, associated with the network arcs, with information about the vehicle capacity, the node sequence of each line, the frequency of each line, the default speed for line segments without associated flow function, the time spent at line stops, etc.;
database of the transportation demand; the database organises in matrix, in vector, and scalar form the quantity of origin-destination trips between the centroids of the 566 zones the city territory is divided into; the centroids are a sub-species of the nodes and are linked to the transportation network by fictitious arcs; the information source about the origin-destination trips is the population census, for the ordinary (daily) trips for work or study purposes, and two specific surveys made by 5,000 interviews, respectively to residents within the peripheric highway GRA) and to car divers entering the area within the GRA.

In addition to the data from the air quality monitoring network, described in the chapter on air quality, data about the meteorological conditions were surveyed with sophisticated instruments in order to establish a correlation between those conditions and the air quality parametric values and then to be able to predict in a more detailed way the evolution of pollution phenomena.

The survey instruments were used in order to measure the air temperature, the wind direction and speed and then to detect the position of thermal inversion layers. These instruments are very sensitive, able to detect very thin thermal inversion layers, and allow very detailed meteorological provisions. They consist in:

a tethered balloon, equipped with instruments for in situ measurements, in order to evaluate the accuracy of the two other instruments, using remote sensing technologies;
a SODAR REMTECH PA2, which consists of a Phased Array antenna with 196 elements, a transmitter-receiver, an acoustic amplifier, and a data acquisition system; the SODAR works by emitting acoustic impulses,with a specific amplitude and phase for each element of the antenna; from the combination of the impulses, three acoustic beams can be obtained, with limited acoustic intensity, required by the urban environment; the acoustic impulses are then reflected by the air layers and received by the instrument, which is able to calculate, from the intensity of the return echo, the wind speed in each of the three components, the standard deviation of the vertical and horizontal wind direction, and the height of the thermal inversion;
a radiometer ATTEX MTP-5, which consists of a high sensitivity receiver, a scanner, a control unit, and works by emitting radio signals with different angles, which are then reflected by the air layers; from the comparison of return signals with different angles it is possible to define the vertical temperature profiles.

Methods

The implementation of the EMME2 Model.

The transportation demand, represented by the quantity of origin-destination trips between each couple of zones the city territory is divided into, is attributed to the arcs of the transportation network in order to optimise the transportation time. The implementation requires the calibration of functional parameters, by comparison of calculated values with surveyed values, at selected locations; moreover, it requires the definition of correction factors to improve the likelihood of the results.

The implementation of the ATMOSFERA System.

The availability of very detailed meteorological data allowed one to use two types of predictive models, integrated in a forecasting system called ATMOSFERA, based on the statistical analysis and elaboration of time series about pollution and meteorological parameters:

ARIMAX model (autoregressive moving average models, with integrated use of exogenous variables);
Neural Network model, able to improve the prediction by learning from the time series (the longer the time series, the better the prediction).

The system is able to establish correlations between the conditions of stability of the atmosphere (due to thermal inversion phenomena) and the air quality in the city or in zones close to specific air quality monitoring stations. From such a correlation, and from the prediction of the evolution of the meteorological conditions, it is possible to predict the evolution of the air quality.

Results

The ATMOSFERA System.

The implementation of the ATMOSFERA System allows the availability, every day, of forecasts about the concentrations of pollutants (CO, NO_x, O₃, SO₂). The forecasts are available both for each of the twelve monitoring stations located on the territory of the city (see chapter on air quality) and as a synthetic index for the whole city. The ATMOSFERA System is developed, as scientific computer software, in the SAS environment, and makes available in real time the above described forecasts in tabular and graphical form (diagrams, bar charts, etc.).

The implementation of the EMME2 Model made available information about the quantity of vehicles in each arc of the transportation network, both during rush hour and during the whole day. Such information is available both in numerical and in graphical form as maps of the transportation network at the present time and for future scenarios of the development of the city and its transportation network. The traffic loads in each arc of the network, and for each temporal scenario, are represented by a scale of thickness of the segments representing the arcs.

Uses

Based on the improved knowledge by the above data and methods, programming provisions and operational interventions in the transportation system and related sectors were realised. The programming provisions and operational interventions are represented by thematic maps. The most representative are described below.

Classification of the arcs of the street network, according to their suitability for the transportation functions, within the peripheric highway (including an area of about 365 km²). Such a classification, and the related map, is the synthetic documentation of the Master Plan of the Urban Traffic, approved by the city government in October 1997. The categories of the classification are: urban highways (81 km), fast trafficways (172 km), quarter streets (493 km), and local streets, the last one available for pedestrians and parking.
Definition of four concentric zones of different modal split (historic centre, public transportation and residents’ private cars; within the railway ring, incentives to switch from private car to public transportation and disincentives to use private cars; dense residential area, transportation shared between public and private; external area, mainly private cars).
The zone subject to traffic block in case of alarm warnings.
The zones of parking tariffs along the streets
The protected lanes, admitting only public transportation.
The network of new fast tramway, railway, and subway lines.
The Parking Plan.
The restricted street/squares, exclusively or mainly for pedestrian use.
The regulations for tourist busses.

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 loads in the 4068 arcs of the street network	The territory of the city	analog map	Subdivision of the territory of the City into 479 zones, and of the external territory into 79 zones use of the Census data about trips for work or study (daily trips), organised in matrix, vector or scalar form, as origin destination trips between the 479 + 79 zones; estimation of the extraordinary trips by field survey and data organisation as origin-destination trips implementation of the EMME2 Model, with modal split of the origin-destination trips among transportation modes, using a Logit Multinomial Model attribution of the origin-destination trips to the arcs of the street network and of the public transportation network, in order to optimize the transportation time calculation of the traffic loads, in the rush hour and in the whole day, at the present time and at the year 2001 scenario	individual daily trips for study or work individual non daily trips (1988; 1991) dimensional and functional characters of the street network dimensional and functional characters of the railway/ subway network dimensional and functional characters of the vehicle fleet	sample of 4,200 trips for the calibration of the Logit Multinomial Model sample of surveyed traffic loads on representative urban arteries, for the calibration of the EMME2 Model	Census time (1991); Survey in a specific time period; Technical transportation data gradually updated	group of Census units; arc of the street or railway-subway network;
	A.T.M.O.S.F.E.R.A. air quality forecasting system	The territory of the City The reference area of the monitoring stations	forecasts presented in tabular and graphical form (diagrams, bar charts)	The availability of very detailed meteorological data allowed to use two types of predictive models, integrated in a forecasting system called A.T.M.O.S.FE.R.A, based on the statistical analysis and elaboration of time series about pollution and meteorological parameters: ARIMAX model (autoregressive moving average models, with integrated use of exogenous variables) Neural Network model, able to improve the prediction by learning from the time series (the longer the time series, the better the prediction) The system is able to establish correlation between the conditions of stability of the atmosphere (due to thermal inversion phenomena) and the air quality in the city or in zones close to specific air quality monitoring stations. From such a correlation, and from the prediction of the evolution of the meteorological conditions, it is possible to predict the evolution of the air quality.	the following parameters are surveyed by remote sensing and from in situ measurement air temperature wind direction wind speed humidity pressure solar radiation rain height of the base of the first inversion aloft wind speed and direction profiles up to 500 m of altitude		continuous measurements: at ground level in-situ at the meteorological stations in the layer up to an altitude of 500 m by means of remote sensing instrumentation	n.a.