# Transport Systems and Mobility for Smart Cities
## 2 Literature Review
### Mobility and Transportation Systems: Present Challenges  
The transportation ecosystem is becoming increasingly complex, particularly in big cities with a huge increase in transport demand implying urban mobility that is dominated by private cars. This results in an increase in road traffic and causes problems in mobility such as congestion, environmental pollution, noise, and traffic accidents, which directly affect the quality of the urban mobility services and reduce the levels of accessibility and urban mobility. Additionally, this contributes to increased delays and energy expenditure, pollution, and stress, which in turn decrease productivity and lead to higher living costs for society. Car accidents remain one of the biggest concerns. In the EU-28, these account for more than 20,000 fatalities and 100,000 serious injuries every year [10]. Mobility flows are a proxy for understanding human activity in urban space, playing the role of a prime driver for sustainability, as well as the main integrator of the flow of objects and people, and also supporting the flow of information. The nuclear duty of the transport system is, therefore, to provide timely and safe mobility under environmental protection, to assume new methods of mobility, and to integrate different users' expectations and evolution--particularly for the young, elderly, and less able people who are considered the most vulnerable road users (VRUs). In addition, the transport system must make the transition to mixed traffic environments with the coexistence of present and future connected and automated vehicles (CAVs). The introduction of CAVs is regarded as crucial by the European Commission to achieve the 2050 goals of reducing GHG emissions by 60% and, in line with Vision Zero, to have close to zero fatalities in transportation [11]. Nevertheless, it has become clear that the positive impact that CAVs can bring for sustainability and safety will have to first withstand the challenges of coexistence with conventional modes of transportation and the challenge of transitioning to mixed traffic environments including both \"acceptance, trust and reliance on automation\" and \"the role of humans in emergencies [12]. Concerning the support to meet any challenges, the focus is placed on having relevant and updated data and information. Thus, in addition to the rising data acquisition capacity and intelligence of vehicles, the development of a global system of sensorization in transport and mobility infrastructure components is essential through innovative digital technologies, used in a multidisciplinary environment, and including mobile technology, in order to observe all types of movements of vehicles and people, and to consider the users. This system will need to capture relevant data supporting the production of essential information to support the integrated management of the mobility system, as well as to give answers to the global decisions on the city environment (noise, air quality). The information produced can also support the development of key performance indicators that support decision making in several fields, focused on the current mobility operation and optimizing the global mobility and transport system, as well as developing alerts under scenarios of severe and unpredicted threats. Mobility relies on users, vehicles, and transport infrastructures where different threats that can cause disruption should be considered, such as natural disasters (hurricanes, floods, fires) or human-made events such as terrorist attacks, cultural events, strikes, and systems failures caused by human error or mismanagement. Thus, the resilience of the transportation system should be carefully analysed to test its capacity to absorb and/or reduce impacts of different disturbances as well as the capacity to maintain and/or restore its normal operation to an acceptable performance level within a timeframe and cost that are considered acceptable [13,14].