Why Are Subways Built Underground in Cities?

The decision to build subway systems underground in urban areas is multifaceted, influenced by historical events, practical considerations, and design principles. This article explores the reasons behind the underground construction of subways, the challenges of deep underground digging, and the potential consequences of encountering water.

Historical Context and Weather Protection

Subways as a form of transportation have a rich history, with one of the earliest examples recognized in New York City. The shift towards underground mass transit began after the Great Blizzard of 1888, which paralyzed the city and led to the deaths of countless people and animals due to the extreme weather. Engineers realized that stations and trains constructed underground would be protected from such harsh conditions, ensuring safer and more reliable transportation services.

Understanding the Term 'Subway'

The term 'subway' comes from the Latin root meaning "below" or "under." It refers to a public transportation system located underground, distinct from above-ground walkways or elevated railways. Just as a submarine dives beneath the water's surface, a subway dives beneath the ground, providing a protected and efficient means of transportation.

Practical Considerations

There are several practical reasons why subways are built underground:

Minimizing Traffic Disturbance: Underground construction helps minimize traffic disruptions by providing an alternative to above-ground routes, which can impede vehicular and pedestrian traffic. Preserving Property Values: Subways do not negatively impact the value of real estate, as they are out of sight and do not obstruct views or access. Operational Reliability: Weather-related disruptions, such as snow and ice, are minimized, ensuring consistent and uninterrupted service.

Digging Deep: Potential Challenges and Consequences

While the benefits of underground construction are clear, there are also potential challenges, particularly when it comes to digging deep below ground. Here are some of the most significant issues:

Encountering Water: Many subways in New York City, particularly those located below the water table, require extensive waterproofing and pumping systems to ensure optimal operation. Increased Costs: Tunnels that pass beneath rivers or bodies of water under pressure are significantly more expensive to construct due to the additional challenges involved. Urban Design Solutions: In some cases, subways may need to rise above ground to navigate natural obstacles or to align with existing infrastructure. For example, the Manhattan Bridge in New York City offers passengers a unique above-ground experience.

Case Study: New York City Subway

New York City serves as an excellent case study for subway construction, featuring a diverse range of underground, elevated, and above-ground transit systems. Here are a few notable examples:

Underground Stations: The majority of the New York City subway system is underground, with numerous subway lines running through the city. Examples include the Broadway Line and the 4th Avenue Line, which are entirely underground until the Manhattan Bridge. Inclined Stations: Some stations, such as the Smith-9th Street station, rise to a higher elevation above ground, making them unique and providing scenic views of the surrounding area. Above-Ground Sections: To navigate over rivers or natural obstacles, the subway system includes above-ground sections. For instance, the Broadway line travels at ground level over the Gowanus Canal before descending into the subway tunnel.

Conclusion

The decision to construct subways underground is driven by a combination of historical events, practical considerations, and design principles. While the challenges of deep underground digging and the potential consequences of encountering water must be carefully managed, the benefits of underground construction in terms of weather protection and operational reliability make it an invaluable part of modern urban infrastructure.