## 1 Introduction  
In the European Union (EU), transport is a key economic sector with an estimated EUR 599 billion in gross value added (GVA) for the transport and storage services or 5.0% of total EU GVA in the EU-27 in 2018 [1]. It represents 19.5% of the total greenhouse gas (GHG) emissions [2] and is the only sector that has not seen a decrease in GHG emissions between 1990 and 2018 [3]. In 2019, transport represented 30.9% of final energy consumption [4]. Transport systems include physical and organizational elements and are in general intrinsically complex. These elements influence each other directly and/or indirectly, linearly or nonlinearly, and may have feedback cycles [5]. As [PERSON] [6] argues, the transport system can be considered as a complex, large-scale, interconnected, open, socio-technical system, including elements from the built environment and the social-political domains. In this sense, any change in a transport subsystem, even if predictable separately, can be difficult to predict or even be counterintuitive, when considering the interactions, especially with the users. This is easy to comprehend considering that the nature and extension of the relationships in the interrelated elements of such a system are usually not easily identifiable in terms of their directionality, magnitude, and time scales [7]. In addition, any organizational innovation including new mobility concepts that do not require hardware modifications can be also regarded as a new technology since they aim to use hardware in a different manner [8]. In parallel, the technological applications across the various transport systems have been increasing in numbers and level of complexity along with the overall technological development in related sectors (energy, information and communication technology, etc.). In fact, digital technologies, connectivity, and social media are transforming traditional concepts of mobility [9; 10; 11]. New mobility services and concepts are emerging, such as mobility as a service and cooperative, connected and automated mobility, and give rise to innovative mobility services [12; 13; 14]. Smartphone applications offer real-time analytics and data on traffic conditions [15]. Technology-driven eco-driving solutions can have a positive influence on fuel efficiency [16]. Smart parking solutions allow people to optimize time, and reduce fuel consumption and carbon dioxide emissions [17]. New forms of freight delivery appear as viable alternatives, with drones nowadays proposed for the (last-mile) delivery of goods [18]. Crowdsourcing and sensors in cars can be used in the future for monitoring the condition of the transport network [19]. Hyperloop technologies have the potential to revolutionize long distance trips [20]. At the same time, decarbonising transport will require an increase in the production and use of biofuels in all transport sectors, especially in aviation [21; 22] and waterborne transport [23; 24; 25], together with a further diffusion of electric (light) road vehicles [26], with the role of current and future policies being crucial. Regarding sustainable alternative fuels, the role of biofuels and advanced biofuels (produced from feedstocks) between 2040 and 2050 will be very relevant [27]. However, transport sectors are characterized by different levels of innovation capacity, something that has to be taken into account in policies targeting innovation [28]. Another aspect of the challenge is that public policy priorities in the aftermath of the COVID-19 pandemic will need to adopt measures that stimulate innovation in transport technologies and services, supporting in particular active travel, public transport, railways, and aviation [29]. With this perspective, technological developments are fundamental in order for the transport sector to address current and future socio-economic challenges. These developments will be achieved through targeted research and innovation (R&I), which will lead to new quality standards in relation to the mobility of people and goods [30].