Green tunnel solutions. An overview of sustainability trends in the last decade (2013–2022)

In the last decade, green solutions for road tunnels have steadily emerged in the field of engineering. The focus has been on using renewable energy sources to conserve energy and address issues of disaster risk management, territorial resilience and vulnerability, especially as these issues relate to critical infrastructures (CIs), such as roads and railways. Focusing on the equilibrium of the infrastructure through integrated system services and their external effects guarantees a better evaluation of both effects as they relate to other systems and energy consumption optimisation. To this end, a systematic literature review has been conducted herein that collects and analyses studies carried out in the last decade that relate to green energy solutions in tunnels. Upon a review of the Scopus database from 2013 to 2022, 46 conceptual and empirical studies were selected. Classifications and discussions were then developed according to the main issues identified (e.g., energy saving in road tunnels, zero-energy tunnels, renewable energy sources, tunnel safety lighting, and sustainable infrastructure). Each contribution constitutes a part of the current literature that combines the problems of tunnel safety (as represented by the energy costs of safety devices, e.g., tunnel lighting systems) with issues of renewable energy sources in tunnels. The results of this systematic review offer ideas for future directions of the ‘green’ vision for tunnel infrastructure. This study represents the state-of-the-art of renewable energy solutions currently present worldwide. Gaps in the literature that have yet to be addressed include how to build a green system as well as how to balance its life costs. The review supports the claim that the integration of renewable energy sources can exploit innovative solutions related to the concept of resilience.