## 7 Conclusions and Future Work  
We have presented one approach to the combined use of virtual traffic lights and urban platoons, which may be easy to realize in the short term thanks to the advances in the areas of connected cars and autonomous driving. Our proposal tries to bring the benefits of platooning to the urban environment, managing maneuvers at the intersections with the help of VTLs and promoting new vehicles to join the platoons by disseminating notifications of arrival along their routes.  
By means of simulation experiments, we have shown that VTLs and platooning entail the potential to achieve substantial savings in travel times and fuel consumption, not only benefitting the vehicles that participate in platoons, but also improving the overall fluency of the traffic. In contrast, unlike what happens in highways, deploying platooning mechanisms alone with traditional signaling would not yield significant advantages, because the size and the dynamics of city roads do not give many opportunities for platoon join maneuvers--they must be sought and facilitated at the intersections, as indicated by our concept of \"_intersection intelligence_\". We have also seen that the extensive coordination among vehicles can be attained with vehicle-to-vehicle communications only (i.e., without resorting to the infrastructure of cellular networks as in [29]) thanks to the good performance of the VaNetLayer and VNIBR protocols.  
As part of our ongoing work, we are investigating possible extensions of the proposed VTL & platoon management logic to work with several priority levels. This would allow, for example, ensuring green lights systematically to emergency vehicles. Likewise, public transport, electric, hybrid and high occupancy vehicles could have greater priority levels than regular cars, and they would be favored if the VTL protocol looked at the priority sums in each lane rather than the number of vehicles. We are also seeking to formalize strategies for the integration of the platoon announcement system with GPS navigators, so that the vehicles can modify the routes they intended to follow to enjoy more efficient and comfortable rides. Finally, we are working to categorize and resolve the potential security breaches of our protocols, from the virtualization to the application layer, to prevent misuses and malicious network attacks that could lead to safety threats. We believe that the blockchain architecture presented in [40] can be a good framework for a cohesive solution, that could actually benefit from the infrastructure of virtual nodes that underpins our work.  
**Author Contributions:** Conceptualization: [PERSON], [PERSON], [PERSON] and [PERSON]; methodology: [PERSON]; software: [PERSON] and [PERSON]; formal analysis: [PERSON] and [PERSON]; writing--original draft preparation: [PERSON], writing--review and editing: [PERSON]; supervision: [PERSON], [PERSON] and [PERSON]; project administration: [PERSON], [PERSON] and [PERSON].  
**Funding:** This work has been supported by the European Regional Development Fund (ERDF) and the Galician Regional Government under agreement for funding the Atlantic Research Center for Information and Communication Technologies (AtlantTIC), and by the Ministerio de Educacion y Ciencia (Gobierno de Espa) research project TIN2017-87604-R.  
**Conflicts of Interest:** The authors declare no conflict of interest.