# Faudistic Platooning: Subdivide Platoons, Unite Networks, and Conquer Efficiency and Reliability
## 1 Introduction  
Platoons are convoys of several vehicles in which the first vehicle is driven manually and the following vehicles are automated. Automation within a platoon takes both longitudinal and lateral control into consideration. The benefit of platooning is linked to the distance between two following vehicles, i.e., the inter-vehicle distance. The inter-vehicle distances are down to approximately 10 m, which is smaller compared to human driving. This reduce aerodynamic drag and thus, energy consumption. Even smaller distances do not reduce energy consumption significantly more but may introduce cooling problems, especially for heavy goods vehicles (HGVs) [1]. Although platooning is mainly considered for HGVs, it is not necessarily limited to them.  
The aerodynamic drag is responsible for approximately a quarter of the energy consumption for an HGV. This causes approximately one third of vehicle life cycle costs. According to the industry, any technology for long-distance haulage that promises energy savings is already considered to be worth investigating from a level of 0.5% [2].  
Research has shown that the energy-saving potential for various vehicle types is significantly above the 0.5% savings threshold [3]. Depending on the position within the platoon, energy savings between 2.8% and 9.7% per vehicle are possible. Even theleading vehicle benefits from platooning and saves between 2.7% and 5.3% consumed energy. Team energy savings, i.e., savings of all vehicles within one platoon, at a distance of approximately 9 m and a velocity of approximately 90 km h\({}^{-1}\) reach 3.7-6.4% [4].  
Furthermore, platooning augments the road capacity, i.e., the maximum number of vehicles per unit of time that have a reasonable expectation of passing over a particular roadway component under prevailing roadway and traffic conditions [5]. Depending on inter-vehicle distance and the number of platooned vehicles [6], road capacity can be significantly increased due to the closer spacing and smoother driving behavior among vehicles within the platoon. The authors show as an example, in [7], that road capacity is increased by 11.5% when only 12% of the vehicles are in platoons of six vehicles. Higher percentages of platooned vehicles or platoons consisting of more vehicles further increase road capacity.  
Platooning is more than longitudinal and lateral automation. However, status and intent must be shared, and agreements need to be found [8]. Platooning can be seen as a three-layered system [9]: the transport layer distributes the goods over the available vehicle capacities and assigns their routes. The platoon layer performs platoon management, i.e., forms, maintain, dissolve, and perform maneuvers. Finally, the vehicle layer performs real-time vehicle control, including longitudinal and lateral control, and is responsible for safe operation.  
All layers require communication either between infrastructure and vehicle or between vehicles. Different layers have varying requirements on the quality of service of the communication network. Requirements with respect to availability, reliability, end-to-end delay, and data-freshness go hand in hand with the impact of each layer in the safe operation context. For example, data on the vehicle layer is of small payload as it mainly contains vehicle state information, but it must be sent with high frequency and received on a timely and reliable basis. In contrast, data on the transport layer has a greater payload but needs to be sent less frequently. Package losses here can be absorbed and compensated for.