Funding for this research was provided by:
Klima- und Energiefonds (B464789)
Bundesministerium für Verkehr, Innovation und Technologie (860929)
Received: 27 August 2018
Accepted: 24 June 2019
First Online: 2 July 2019
Ethics approval and consent to participate
: The study was conducted according to JOANNEUM RESEARCH’s ethics guidelines.
: Not applicable, since the study reports only aggregated data.
: The authors declare that they have no competing interests.