# An Overview of Cooperative Driving in the European Union: Policies and Practices
## 4 Current State of the Art of C-ITS Systems
The main advantage of the above organisation, based on different building blocks, is that each element is easy to manage and maintain since it is independent and self-contained. Indeed, a modular approach has similarly been adopted for the development of testbeds proposed in [49] and [50]. The former is based on a software-defined radio (SDR) platform and aims to satisfy the most stringent link-level communication requirements for V2X applications, especially in the case of time-critical tasks such as emergency braking and cooperative emergency manoeuvres. The latter represents a communication-centric traffic light controller system based on the following major components: theRSU integrated with the smart traffic light manager (STLM) module, which is responsible for the creation and transmission of SPaT and MAP messages; the OBU with the human-machine interface (HMI) displaying information in a user-friendly way; the traffic light power manager (TLPM) module, which provides the required power for traffic lights and allows them to be controlled remotely; and the traffic management curve (TMC), which monitors and manages traffic flows, thus contributing to decreased traffic jams. A testbed specifically developed for WTC applications was presented in [51]. It was devised by the Finnish Meteorological Institute (FMI)and Lapland UAS (Lapland University of Applied Sciences), and it was tailored for typical arctic winter conditions (i.e., snow and ice). In particular, the central element was represented by a combined road weather station (RWS)/RSU hotspot, which employed IEEE 802.11p communication as the primary channel. Therefore, vehicles exchanged data with the RSU during bypass, or whenever in communication range with it, and could further transmit such information to vehicles they met outside the catchment area of the RSU. However, if IEEE 802.11p communication was not available, vehicles could obtain information also by means of traditional Wi-Fi communication or, as a last resort, a 3G cellular link to obtain current data from the nearest RWS. A testbed based on a system configuration specifically developed for vehicle platooning applications, instead, was described in [52]. It relied, exclusively, on V2V communication by means of 802.11p and 5G-V2X vehicular technologies without the use of sensor data. Although vehicle platooning applications generally envisage that both the leader and the followers send standardised messages, in this work the communication was considered unidirectional (i.e., it occurred only from the platoon leader to the follower). It was based on CAMs, which comprised header, payload, and platooning container, while the control algorithm adopted for calculation of desired acceleration and steering angle to follow the vehicle in front was based on a model predictive controller (MPC). Moreover, application of such a service in two urban scenarios, namely fast lane change and turning manoeuvres, was presented. Additionally, [53] presented the WiSafeCar platform for testing accident and weather condition-related services. It was based on four main components (i.e., vehicles, the RSU, the linking point, and a mobile user) and relied on an intelligent hybrid wireless traffic safety network. IEEE 802.11p communication, together with a supporting 3G cellular network, was implemented. Moreover, the possibility of exploiting vehicle-based sensor information and observation data for providing real-time services was also investigated. Finally, it is worth citing two works that provide considerable contribution to the development of vehicular networks. The first presented a real-world testbed called HarborNet [54], a vehicular mesh networking testbed that comprised OBUs installed in trucks, administration vehicles, tow boats, and patrol vessels; RSUs connected to the optic fibre backbone of the seaport; and cloud-based data and control systems.