# IoT-Enabled Smart Cities: A Review of Concepts, Frameworks and Key Technologies
## 3 Review of IoT-Enabled Smart City Components and Solutions
### Smart Mobility and Transportation  
The smart mobility and transportation concept implies the shift from traditional transportation systems to Mobility-as-a-Service (MaaS), where a smart IoT infrastructure connects different actors (citizens, public administrations, private companies) and entities (vehicles, personal devices, city sensors, actuators, etc.) [70]. IoT and intelligent transportation systems (ITSs) [71] allow the provision of smart applications and services to manage, for instance, private and public traffic flows, dynamic traffic routing, smart parking, vehicle sharing and sustainable mobility, connected driving, etc. Intelligent traffic solutions often rely on the application of predictive models for early warnings, accident prevention and real-time traffic congestion management.  
In this context, many IoT network technologies have been proposed and used. City sensors and actuators (e.g., for the management of traffic lights, digital signage, road barriers, etc.), location-based GPS services and mobile-to-mobile communication are the basis for the implementation of vehicle-to-vehicle communication (V2V) and vehicle-to-infrastructure communication (V2I). Additionally, 5G networks and LTE-based systems have been employed for vehicle-to-everything (V2X) services [72]. Vehicular ad hoc networks (VANETs) [73] have been designed to handle a large number of nodes (including vehicles, roadside units (RSU) and on-board units (OBU) [74]) and present a good adaptability to the frequent topology changes and the data exchange rate [75]. The adoption of ITSs is at the basis of smart parking and car sharing [76] services. The most disseminated devices are RFID tags, infrared and ultrasonic sensors, smartphone-based sensors, video cameras for smart parking [77] and on-board diagnostic systems (OBD tools) [78].  
In Berlin, the smart mobility service Jelbi was introduced in 2019, based on a mobile application that is connected to all services provided locally (e.g., car-sharing companies such as MILES and DB Flinkster and e-vehicle hire companies such as TIER), to foster the passage toward a more sustainable mobility [79]. In Florence, the Snap4 City platform has been developed in the context of the Sii-Mobility project for sustainable mobility, providing a flexible IoT smart city platform and several applications to manage heterogeneous and complex urban mobility scenarios by integrating city sensors/actuators and IoT/IoE [34]. Atlanta has powered its transportation infrastructure with many smart technologies. For instance, a system of adaptive traffic signals that adjust to traffic conditions in real time are installed on the North Avenue Smart Corridor (a critical longitudinal communication roadway) [3]. London has a cycle rental system, currently offering more than 11,500 bikes and over 750 docking stations. As for car-sharing solutions, London has six active operators in the city, covering the whole Greater London area [80]. In addition, London's public transportation system provides the use of Oyster cards, which are smart electronic cards that exploit RFID technology and can be used for paying and buying electronic tickets for public transportation, thereby reducing queues and eventually tracking users' flows. In Santander, smart mobility services are applied to the management of public transportation, outdoor parking management and traffic routing [81]. The city of Bilbao has enhanced the sustainability of local mobility by deploying a network of e-bikes with 40 pick-up points and e-buses that are supported by mobile applications: GeoBilbao (reporting real-time information about parking and traffic status) and iBilbbus (information about bus stops and schedules) [66]. In Seoul, the Gangnam ubiquitous district has a centralized control framework, including the Transport Operation and Information Service (TOPIS) app and the \"Owl Bus\", which is an innovative bus service performing analytics on the big data that is collected on-board [82].