Control theory has played a crucial role in the development of the various fields of the human activity, and it is also thanks to the control applications if nowadays we have more and more safe and efficient transport systems. Indeed, besides the numerous advances in the automotive sector, in the last decades several control techniques have been successfully applied to road traffic systems in order to reduce traffic congestion and more in general to minimise the journey times.
The application of strategies such as ramp management, mainstream control and route guidance have really contributed to improve the operation of road networks, yet nowadays traffic control strategies cannot be limited solely to the mitigation of congestion phenomena, but must take into account the pressing need of environmental safeguard and human health protection. A recent survey developed by the World Health Organization estimates that in 2012 there were 3.7 million of premature deaths caused by the environmental pollution, most of which may be attributed to the prolonged exposure to substances resulting from the use of fossil fuels. Therefore, the responsibility of road transports with respect to the damages caused by the emissions of pollutants and greenhouse gases cannot be neglected and this awareness implies a revision of the traditional control strategies towards a more sustainable perspective vision. A new challenge for the researchers in the field of traffic control consists in definition of control strategies that integrate the efficient use of the road network capacity with the minimisation of emissions, fuel consumptions, noise, accidents, and so on.
The revision of the most popular traffic control strategies in an eco-friendly perspective can certainly contribute to mitigate the environmental impact caused by the ever-increasing traffic volumes (an overview of sustainable control strategies in freeway networks is reported in ). Yet, the recent technological advances in matter of vehicles and communications systems pave the way to innovative control schemes that can further improve the sustainability of the traffic systems of the next future.
Indeed, advanced technologies such as Vehicle-to-Vehicle (V2V) and Vehicle-to-Infrastructure (V2I) communication systems can give rise to a connected environment in which some information on traffic conditions, detected in real time, can be directly transmitted to the drivers on board of the vehicles. This possibility to directly communicate with single vehicles can be further exploited making the vehicles themselves actuators of control strategies which positively influence the entire traffic system.
Even more ambitious technologies concern the introduction of autonomous or semi-autonomous vehicles, whose penetration rate in the traffic streams can significantly change the concept of mobility as it is commonly perceived both in the urban context, giving rise the so called Smart Cities , and in the extra-urban contest (see for instance ). Obviously, considering the wide variety of automated vehicles and their possible applications , it is not straightforward to estimate the real effects due to the introduction of a high level of automation in vehicles; therefore the debate on the possible opportunities and disadvantages related to the efficiency of the entire traffic flows is still open. Yet, it is also reasonable to assume that intelligent vehicles, specifically designed with the aim to overcome the drawbacks related to the human driving and then intrinsically safer and more efficient than conventional vehicles, can influence traffic dynamics, improving safety and reducing energy consumption and the related environmental effects.
Regardless of what the future traffic scenarios will be, whether they are traffic environments dominated by autonomous vehicles or characterized by a mixed traffic in which traditional and intelligent vehicles will coexist, the role of traffic controls will continue to be crucial in order to best combine the mobility needs of road users with the need to protect the quality of life of humans and of the environment.
 Ferrara, S. Sacone, S. Siri (2018). Control Strategies for Sustainable Mobility in Freeways. In Freeway Traffic Modelling and Control, Advances in Industrial Control Series, Springer, chap. 10, 269-291.
 G. Cassandras (2017). Automating Mobility in Smart Cities. Annual Reviews in Control, 44, 1-8.
 E. Shladover (2005). Automated Vehicles for Highway Operations (Automated Highway Systems). Proceedings of the Institution of Mechanical Engineers, Part I: Journal of Systems and Control Engineering, 219, 53-75.
 Diakaki, M. Papageorgiou, I. Papamichail, I. Nikolos (2015). Overview and Analysis of Vehicle Automation and Communication Systems from a Motorway Traffic Management Perspective. Transportation Research Part A, 75, 147-165.
Dr. Cecilia Pasquale
Department of Informatics, Bioengineering, Robotics and Systems Engineering, University of Genova, Genova, Italy.
IFAC T.C. 7.4