Besides the rise of sustainable technologies, successful sustainability transitions crucially depend on the phase-out of unsustainable ones. However, the detailed dynamics of declining technological innovation systems (TIS) remain vague. Thus, based on the new TIS life cycle framework, we investigate how the technological dimension of a mature TIS adapts to increasing transformational pressures towards its decline. Considering the internal combustion engine (ICE) as a suitable research case, we measure the technological adaptation as changes in the dominant technological trajectory over time and across TIS territories. Empirically, this is operationalised by a main path analysis in patent citation networks, using 221,700 patents to cover the period from 10 January 1901 until 31 January 2019. Our results not only point to considerable shifts in the direction of technological development over time but also highlight stark differences across the three major car markets. Most notably, in contrast to USA and Japan, where hybrid powertrains have become the dominant alternative powertrains, the dominant trajectory in the EU territory points to an ongoing commitment towards diesel technology. In essence, our results highlight the importance of path dependency and connectivity of the knowledge search process as well as selective forces on the innovation system level, which have been neglected by related empirical studies. Conceptionally, our analysis demonstrates that the technological adaptation process is influenced by specific developments during a time period and heterogenous territorial dynamics within the TIS. Consequently, future TIS studies might consider spatially heterogeneous development cycles as well as possible mechanisms to establish an international trajectory towards sustainability goals.
