Grey infrastructure

Engineered physical structures that underpin energy, transport, communications (including wireless and digital), built form, water and sanitation, and solid-waste management systems and that protect human lives and livelihood.


1. Grey infrastructure may be interpreted more narrowly to refer to subsets of the above definition.

2. See also "Infrastructure".


IPCC, (2022). Annex II: Glossary [Möller, V., R. van Diemen, J.B.R. Matthews, C. Méndez, S. Semenov, J.S. Fuglestvedt, A. Reisinger (eds.)]. In: Climate Change 2022: Impacts, Adaptation and Vulnerability. Contribution of Working Group II to the Sixth Assessment Report of the Intergovernmental Panel on Climate Change [H.-O. Pörtner, D.C. Roberts, M. Tignor, E.S. Poloczanska, K. Mintenbeck, A. Alegría, M. Craig, S. Langsdorf, S. Löschke, V. Möller, A. Okem, B. Rama (eds.)]. Cambridge University Press, Cambridge, UK and New York, NY, USA, pp. 2897–2930, doi:10.1017/9781009325844.029.



Tokyo Bay Aqua-Line, Japan

Tokyo Bay Aqua-Line, also called Trans-Tokyo Bay Expressway, is a bridge-tunnel system connecting the cities of Kawasaki and Kisarazu in Japan. The construction of this system shortened the drive between the two industrial areas from 90 minutes to 15 minutes. It has an overall length of 23.7km, including a 4.4km bridge and a 9.6km tunnel underneath the bay – the fourth longest underwater tunnel in the world. The system also features an artificial island, acting as a rest stop and a ventilation tower, erected above the middle of the tunnel. The structure was designed to withstand earthquakes and typhoons, common disasters in the region. It features reinforced concrete pillars and a system for absorbing seismic vibrations, ensuring the safety and continuity of transport services, even in the event of a disaster.


  • Hotta, K. (2002). Tokyo Bay Reformation. Engineered Coasts, 85-102.
  • Norio, Y., & Toshiyuki, O. (1998). Tokyo Bay Aqualine. Earthquake-proof and wind resistant measures for bridge. Foundation Engineering & Equipment, Monthly, 26(1), 89–92.