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New method developed to find out the emissions of an urban bus fleet

Researchers from INSIA (UPM) have developed a new methodology to evaluate the consumption and emissions of urban buses in Madrid using on-board equipments and statistical methods.

In collaboration with Madrid Municipal Transport Company (EMT) and the Madrid city council, researchers from University Institute of Automobile Research (INSIA) from Universidad Politécnica de Madrid (UPM) have developed ECOTRAM, a model to quantify the pollutant emissions produced by the urban transport.

The model, which has been validated, assesses the effect that certain modifications may have on a bus fleet. This can be of a great help when the time comes to make changes and renovations of the fleet by the local authorities.

Modelling the pollutant emissions produced by mobile sources requires detailed data of the traffic condition of the area to assess. This information might come from either default models for a road network or direct measures with on-board equipments in the vehicles and their later treatment for the estimation of the corresponding emissions factors. This last technique was the method used by the UPM researchers to quantify the emissions of urban buses in Madrid.

After three years of collaboration with EMT and the City Council of Madrid, the INSIA researchers have developed ECOTRAM, a model that has been validated based on the results obtained during the tests carried out on a selection of bus lines considered representative enough of the whole fleet.

In order to select the vehicles for the study as well as the bus lines for the experimental campaign, researchers applied sampling techniques. A cluster analysis was the procedure used to select the set of bus lines. Thus the sets of lines were put together in clusters of similar kinematic variables. As a result, the lines included in each cluster lead to similar average results of both emissions and consumption. Therefore, the results can be extrapolated to the rest of lines of each cluster obtaining global estimations of the whole fleet.

Likewise, researchers took into account numerous variables to select the vehicles of the sampling to measure the emissions and consumption. The measures were carried out on buses of different European emission standards (Euro II, III, IV y CNG) with natural gas, diesel and biodiesel. In addition, in order to study the occupancy levels, they took into account three load states: empty, half load and full load. On-board monitoring equipments of carbon dioxide (CO2) and other pollutants (CO, THC, NOx) were installed in the selected vehicles.

With the experimental measurements, researchers analyzed the emission factors that best relate the emissions and consumption to the kinematic variables of the driving cycle (speed, stop time and slope), the vehicle lodge state and altitude. Finally, these factors were applied and extrapolated to the rest of the lines of the bus fleet obtaining as a result the consumption and emissions of the whole fleet.

According to José María López, a researcher of this project, the ECOTRAM model allows us to accurately assess the effect of possible modifications in the vehicle fleet under study. Some examples of these modifications can be either the type of monitoring, the type of fuel or the route of the bus lines.


Modelling the fuel consumption and pollutant emissions of the urban bus fleet of the city of Madrid, Lopez-Martinez, JM; Jimenez, F; Paez-Ayuso, FJ; Flores-Holgado, MN; Arenas, AN; Arenas-Ramirez, B; Aparicio-Izquierdo, F.  TRANSPORTATION RESEARCH PART D-TRANSPORT AND ENVIRONMENT, 52 112-127; 10.1016/j.trd.2017.02.016 A MAY 2017

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