This chapter introduces the main reasons that motivate this thesis, further developed in Chapter 2. The last section outlines the structure of this dissertation.Demand management measures in suburban areas with a toll highway alternative: impact on travel choices -4 - Diagnosis of the metropolitan mobility and congestionDuring the last 70 years, the world's urban population has experienced rapid growth. The sharp acceleration of the urbanization process is reflected in the fact that the percentage of the world's population living in cities has increased from 30% in 1950 to 55% in 2018. This figure is even higher (around 80%) in developed regions. The United Nations forecasts that 68% of world's population will live in urban areas by 2050 (UN, 2019). This fact has posed and still poses a huge challenge in various fields, including mobility and transportation.The concentration of population and economic activity in limited spaces has led many cities to experience multiple advantages and disadvantages. Cities are major economic centers generating 80% of the world's GDP (Swilling et al., 2013). Advantages of cities include greater access to services and aggregation economies, which generate synergies between different economic actors. In addition, cities are places that enable the transfer of knowledge within society, thereby becoming sources of innovation and creativity (Hajer, 2011).On the other hand, there are also adverse effects and diseconomies of scale in metropolitan areas. For instance, cities entail a high consumption of energy and raw materials (Swilling et al., 2013). Furthermore, the high density of inhabitants leads to high mobility demands not easily covered in a sustainable manner. In this sense, urban transportation results in a series of externalities, such as noise, air pollution, or land consumption among others. The spatial and temporal concentration of trips could also lead to congestion of the transportation network.It is widely demonstrated that congestion imposes high environmental, social, and economic costs on urban areas around the world. In addition, it entails extra energy consumption and economic losses due to an increase in travel times for urban dwellers. In big cities, each driver is estimated to lose more than 100 hours a year due to road congestion. For instance, according to TomTom (2020), in 2019 each driver lost 225 hours in Moscow, 195 hours in Mexico City, 172 hours in Rome, 124 hours in Berlin, or 115 hours in Boston. A report elaborated by INRIX (2020) translates these time losses into economic costs in some countries such as the UK (£6.9 billion), Germany (€2.8 billion), or the US ($88 billion). Christidis and Ibáñez Rivas (2012) estimated the cost of road congestion in Spain at €5.8 billion. In the European Union (EU), road congestion results in productivity losses equal to 1% of GDP annually.Congestion tends to be heavier on the entrances to the city rather than in the downtown area. Among the factors that may explain this fact is that mobility patterns are not homogeneou...