Measuring the monetary value of environmental externalities derived from urban underground facilities: Towards a better understanding of sustainable underground spaces

The development of underground spaces has been regarded as a major contributor to urban environmental sustainability. However, insufficient attention has been paid to the environmental externalities of urban underground facilities (UUFs) due to the lack of a bespoke tool for the identification and monetary valuation of such externalities, resulting in the irrational use of underground spaces. To this end, this study systematically explores the categories of environmental externalities tailored to UUFs, considering both environmental contributions and losses. Furthermore, the framework of the replacement/restoration cost method (RCM) was employed to measure the environmental externalities of UUFs in monetary terms, and the framework was then applied to a series of representative UUFs in China as a case study. The results indicate that the monetary value of the environmental externalities derived from UUFs is non-negligible compared to its construction cost, and the positive externalities dramatically outweigh the negative ones. In addition, there are apparent differences in the constituents of externalities among different types of UUFs. It is found that the effects of energy conservation, air pollution and noise pollution prevention proved to be the main contributions of UUFs to sustainability. This study aims to provide a useful model for the identification and measurement of the environmental externalities derived from UUFs, thus aiding in the decision support of underground space planning, as well as obtaining a sound understanding of the role of underground spaces in sustainable development.