Metro systems have been in use for over 150 years, and new metro lines are still being constructed, either as new metro systems or as expansions of existing metro networks. In many cities the metro system is an essential form of transport to keep the cities functioning. This overview compares the findings of various international studies on metro construction and operation, and the impact that metro systems have on cities. The uncertainties inherent in underground construction, with sometimes uncertain hydro-geological conditions and impacts from nearby existing construction projects, are often apparent during metro construction, and have been widely studied. Similarly, passenger comfort and safety during operation is a topic that has received widespread attention, with the main focus on fire safety, as fire poses the most dangerous risk during operation. More recently, passenger comfort related to indoor air quality and aerodynamic effects has received increased attention. The vulnerability of the running stock and the metro network is a significant factor when determining the safety and efficiency of the metro system. Metro efficiency and reliability have a major impact on the transport, economic, environmental and social aspects of cities. Even though they are designed as separated own-right-of-way transport systems, metro systems strongly influence urban development and drive spatial changes in land use. The combination of metro systems with other urban functions provides great potential for the development of urban underground space and the development of more resilient and efficient urban areas. This in turn has an impact on housing prices and produces wider economic benefits beyond the city. Metro systems have also been shown to affect travel behaviour and have a positive impact on public health and environmental quality, by reducing pollution and emissions, despite the large concentration of passengers present in the metro, which brings its own problems. After an overview of the leading and more recent research topics in these areas, the key research gaps are discussed and recommendations for future research are made.

In the urbanisation process of the past few decades, the use of urban underground space (UUS) has contributed to new town developments in many cities in the world. This offers an opportunity to map out and systematically describe the potential contributions of UUS for transport, land use, economic, environmental and social development in new towns for planners, designers and policy-makers to consider. This review synthesises key papers on UUS utilisation and new town development. It indicates that the requirements of intensive use of land resources, accessibility reasons, avoidance of urban problems experienced in old cities, cultural and modernity considerations, and the goal of building smart, low-carbon and sustainable cities drive UUS utilisation in new developments. Underground spaces have been developed in new towns in various forms, with subway, underground parking facilities and underground utility infrastructure being the more prevalent forms of UUS utilisation, and UUS utilisation in new towns varying in scale. UUS utilisation for new developments may confront many challenges related to various issues: relationships between new towns and old city centres; compact and high-density urban forms; transit accessibility; awareness of the significance of UUS; balance between market forces and government intervention; coordination of development; full utilisation of UUS resources; and decision-making support. Existing practices used in UUS development provide lessons from which to learn.

Many cities in the world have developed metro systems. Metro systems affect urban development in many ways, such as enhancing labour force mobility, increasing urban productivity and promoting urban underground space (UUS) utilisation to accommodate urban functions. This paper explores the relationship between metro systems and urban development, with particular focus on the comprehensive impacts of metro development on the economic, environmental and social development of cities. The contribution of metro systems to urban development has been confirmed by numerous studies in many cities in the world. The positive capitalisation of metro systems is reflected in property values in areas surrounding metro systems, although the impacts may vary spatially, temporally and geographically. In addition, metro systems impact on the natural and built environments by reducing air pollution and greenhouse gas emissions, encouraging new development and urban renewal, sharping urban development and land use, facilitating commercial growth and residential development, promoting the utilisation of UUS, and increasing mixed land use and urban density. However, there are mixed effects, both positive and negative, of metro systems on equality of transit opportunity, accessibility and connectivity, public health, travel behaviour, personal identity, travel experience and safety. This study sheds light on the impacts of metro systems on urban development, and provides important information for urban and transport planners and policy-makers wishing to develop metro systems to support sustainable urban development.

The rapid increase in world population in the 21st century, with associated transport and environmental problems, has encouraged the development of urban underground spaces as an optimal solution in many occasions, including urban renewal schemes. This paper reviews literature on the utilisation of urban underground space for urban renewal to provide a better understanding of how urban underground space can contribute to urban renewal, and of challenges and successes in achieving the goals. The paper concludes that urban underground space present new development opportunities (e.g. land/space supply, less traffic congestion, compact city development, and urban sustainable development) in regeneration of existing urban land. Urban underground spaces, as valuable resources and efficient and effective tools for urban renewal, should be considered by decision-makers for transforming existing urban areas, stimulating vibrant and denser development and mixed land use.