# Methodology to Assess Sustainable Mobility in LATAM Cities
## 2 Methodology
### Evaluation of Mobility-Related Performance Indicators
#### 2.2.3 Environmental Impact  
In this phase, an assessment of the urban air quality is performed in connection with the main sources of air pollutants. An analysis regarding on-road vehicles' energy consumption and emissions is essential since they are the most important source of pollution in urban areas [1]. This step results in high importance when evaluating sustainable mobility. Usually, cities have a network of air quality stations for this purpose. Otherwise, the use of low-cost air quality sensors such as purple air [38] can be used for this purpose. Currently, environmental authorities have metrics and methods to grade the air quality in their cities [39]. _Energy consumption_: Analyzing the total of energy consumed by a city by vehicles in a year would be subject to a greater influence on the size of the city than on the performance of their vehicles. Therefore, a better approach is to consider only the vehicle average Specific Energy Consumption (\(SEC_{i,j}\)) or Specific Fuel Consumption (\(SFC_{i,j}\)). For electric-powered vehicles, \(SEC_{i,j}\) is the energy that vehicles of model \(i\) and model-year \(j\) consume while being used, and it is expressed as kWh per kilometer driven. For fuel-powered vehicles, energy consumption can be obtained by the liters of fuel consumed per kilometer driven (\(SFC_{i,j}\)) multiplied by the fuel's low-heating value (\(LHV_{f}\)) as expressed in Equation (1). Aiming to compare the energy consumed by fuel-powered vehicles with electric-powered vehicles, Equation (1) must be multiplied by the thermal efficiency of the thermal power plant (\(\eta_{th}\)) that convert chemical energy into electric energy (known as power plant factor). That factor is around 35% [40]. In this case, \(SEC\) should be named as equivalent specific electric energy consumption. \[SEC_{i,j}=SFC_{i,j}\;LHV_{f}\;\eta_{th} \tag{1}\]  
To determine the vehicle \(SFC\), the average values reported by vehicle manufacturers of the circulating vehicles (per each model and model year) may be considered. However, it is of major interest their real-world energy consumption. The latter approach allows the inclusion of the effect of local conditions such as age deterioration, mechanical condition, driving patterns, among others. Common strategies to measure real-world fuel consumption on a representative sample of vehicles are: (i) measuring the fuel's weight before and after a specific distance driven (gravimetric method), (ii) measuring instantaneous fuel consumption through the On-Board Diagnostic system (OBD method), and (iii) surveying the SFC reported by the vehicles in their dashboard. We recommend the second alternative, which nowadays can be obtained through third companies that provide this service using telematic systems. A detailed description of the measurement of fuel/energy consumption can be found in [41; 42; 43]. _Vehicles' emissions_: An emissions inventory of the anthropogenic emissions is a strategic tool that reports the type and quantity of pollutants that are emitted into the atmosphere by the different sectors. It is essential for the design of actions aimed at the mitigation, adaptation, and control of urban air quality. It identifies the sectors that should be addressed to obtain the highest impact on air quality improvement. However, it requires the measurement of the local on-road emissions to obtain accurate results. The technique used for measuring these emissions, together with the criteria selected for the vehicles sample and measurement conditions, has a great impact on the representativeness of the emissions obtained in each city or country. The most common methodologies to measure on-road emissions can be synthetized in two categories [44]: (i) Fleet-basis emissions techniques, such as Tunnel studies [45], and (ii) Individual-basis emissions techniques such as RSD [46]and Portable Emissions Measurement System (PEMS) [42].