1 Land saving: As the value of urban land in general metropolises is high, building the railway underground can save ground space and make the ground land available for other purposes.

2 reduce noise: the railway is built underground, which can reduce the noise on the ground.

3 Reduce interference: Because the running route of the subway does not overlap or cross other traffic systems (such as ground roads), there is less traffic interference, which can save a lot of commuting time.

4. Save energy: Under the problem of global warming, the subway is the best public transport. Because the subway runs smoothly, it saves a lot of commuting time, makes people happy, and also replaces a lot of energy consumed by driving.

5 reduce pollution: ordinary cars use gasoline or petroleum as energy, and subways use electric energy, so there is no tail gas emission and it will not pollute the environment.

Disadvantages:

1 High construction cost: Due to the need to drill underground, the underground construction cost is higher than the above-ground construction.

Long construction period: it is also because of the need to dig tunnels, lay rails, install equipment and various debugging work. It takes a long time for the subway to start and put into operation.

3 Long lead time: The lead time of subway construction is long, and even testing is needed, because planning and government approval are needed. It takes a very long time from the beginning of brewing to putting it into action and breaking ground. It may be as short as a few years and as long as more than ten years.