The common point is that underground space is becoming a part of the urban structure from the auxiliary part of each project. Therefore, what needs to be calculated is not how many floors can be dug, but whether what is built today is still suitable for the needs of many decades to come?
An underground parking lot, if separated from the public transport network, may not help improve urban traffic efficiency. An underground commercial center that is not conveniently connected to the metro is also difficult to maximize its value. More worryingly, tunnels, technical lines or underground works deployed in advance, if there is a lack of shared data and reserve space, may create conflicts with necessary works later.
International experience shows that an important requirement is that planning, data and coordination regulations are established synchronously with the project preparation process. Singapore has developed 3D underground space planning at Marina Bay, Punggol Digital District and Jurong Innovation District, thereby pre-determining areas that need to be protected for future infrastructure. Japan has its own legal mechanism for the use of deep underground space in large urban areas, in order to serve public works and limit the development of the "come first, use first" type, lacking systemicity.
The noteworthy point is not to build a lot underground, but to pre-establish order of use, corridors to be protected and long-term connectivity. In other words, it is necessary to make room for the future before that space is filled with immediate needs.
From Hanoi and Ho Chi Minh City, this requirement is also worth setting for major cities in Vietnam. Each place has different geology, hydrology, density and development needs, so it is not possible to apply a uniform model. But it is necessary to have sufficiently unified principles on underground construction data, altitude, technical corridors, connection points and reserve space so that projects done first do not hinder projects done later.
The ultimate measure is not the number of basements or commercial areas added, but urban efficiency. Are people's travel more convenient, public transport more attractive, infrastructure less conflicting, and the ground has more space for green trees, walking, and community activities?
The deeper into the ground, the more far-sighted planning must be. Because each space used today not only serves an immediate project, but also shapes the development potential of the city in the decades to come. Doing it right from the beginning, the ground can become a new space fund for the city; fragmented development, the works formed today can become very difficult-to-overcome limitations for urban planning in the future.
