## 2 Materials and Methods  
For this study, the TRIMIS database is used, which covers more than 8000 European or national transport-related R&I projects, including projects from Joint Undertakings and Joint Technology Initiative Programmes. Figure 1 provides an overview of the TRIMIS transport R&I database structure [43]. It is characterized by four distinctive fields (A, B, C, D), with each field containing one or more different tables. The main part (field A) includes the project table, program table, technology table, and organization table. The projects in the database are labelled according to which STRIA roadmap their research is relevant to, with the possibility of being tagged with multiple roadmaps. The TRIMIS technology table derives from the TRIMIS project table. It focuses on technologies researched in European FPs, while, selected projects funded by member states (included in the TRIMIS project database) also are included in the analysis where relevant. The technologies are identified within technology themes through a grounded theory approach [44]. An iterative approach led to the development of a consistent taxonomy for transport technologies and technology themes. Figure 2 provides an overview of the methodology used for the technology assessment of the projects [45]. 1. The results of a study that identified technologies within European transport research projects [46] were analysed. Based on this review, a standardized approach has been established on what constituted a distinct technology and how to label them. 2. All project descriptions were assessed and flagged when a technology was mentioned or hinted. 3. The full list of technologies was evaluated, and the labelling of similar technologies was aligned using also existing taxonomies as a basis. 4. When the technology list was established, a number of overarching technology themes was defined. An extensive list of themes was created and consequently reduced to the minimum number of themes under which all technologies could still be logically placed. 5. The funds associated with each technology were determined by linking them with the total project budget. If multiple technologies were researched in the project, the budget allocated to the technology of interest was determined by dividing the project budget by the number of associated technologies. 6. A set of metrics was established to assess the identified technologies. These metrics are intended to indicate the potential for the technology to be taken forward to  
Figure 1: TRIMIS database structure (adapted from [43]). application through the level of support for its development. Three metrics are relevant to this study:  
* The total value of all projects that have researched the technology (i.e., the total investment, by both the EU and industry, in the development of the technology);
* The number of projects that have researched the technology;
* The number of organizations that have been involved in projects that have researched the technology. Focusing on the metrics (point 6 above), the first two highlight the combined effort that has been put into researching the technology, while the third proxies the level of interest in the technology in industry and academia. Two points are worth highlighting:  
* When identifying the (funding) value to use for a particular project for a particular technology, the total value for the project is divided by the number of technologies that the project has been identified as investigating in order to estimate the 'funding per technology'. Thus, the calculated total funding for the technology should rationally represent the funding for the individual technology. This parameter gives an indication of the total effort that has been employed to bring the technology to its current status and also indicates the level of interest and expectation there is in the potential of the technology. The nature of the funding schemes for the research under which the technologies have been developed is of key relevance to the use of this parameter.