Crazy Rich Singapore | MRT Tunnels, Deep Infrastructure and the Underground City begins with a hidden version of Singapore most people use every day without seeing.
Did you know Singapore’s upcoming Cross Island Line will be more than 50 kilometres long and fully underground, making it the country’s longest fully underground MRT line? At the same time, the North–South Corridor includes a 12.3-kilometre tunnel section, while the city is expanding underground utility, pedestrian and infrastructure networks to preserve scarce surface land.
That makes “Singapore MRT tunnel”, “Cross Island Line”, “underground Singapore”, “North South Corridor” and “Singapore underground infrastructure” powerful search themes. The Crazy Rich story is not simply putting trains underground. It is learning how to use vertical space beneath the city for transport, utilities, water, storage and pedestrian movement.
Crazy Rich Singapore has another city underneath the city.
Did You Know? Underground Space Is a Land-Supply Strategy
Singapore cannot make every road, railway, utility and storage facility compete for surface land forever.
One response is reclamation.
Another is vertical development upward.
A third is to move selected infrastructure underground.
The city becomes three-dimensional.
Why Underground Infrastructure Is Expensive
Building underground requires:
- geotechnical investigations;
- tunnelling machines or excavation;
- ground support;
- waterproofing;
- ventilation;
- fire-safety systems;
- complex utility coordination; and
- continuous monitoring of nearby buildings and infrastructure.
That is why underground space is not automatically better than surface space.
It is valuable when the land saved or the urban benefits justify the engineering cost.
The Cross Island Line: More Than 50 Kilometres Underground
LTA describes the Cross Island Line as Singapore’s eighth MRT line and its longest fully underground rail line at more than 50 kilometres.
It will connect major areas including Jurong Lake District, Punggol Digital District and the Changi region.
The line will eventually include 11 interchange stations.
That means the engineering project is also a labour-market project.
People become able to reach more jobs, schools and services without depending on cars.
Why Interchange Stations Multiply Value
A railway station serves its immediate neighbourhood.
An interchange station connects multiple lines and multiplies route possibilities.
That increases the network value of every line feeding into it.
This is why underground rail should be understood as network infrastructure rather than only tunnelling.
The tunnel is concrete.
The real asset is connectivity.
The North–South Corridor: Road Tunnel Plus Transit Corridor
The North–South Corridor combines road tunnels, viaducts and surface-level changes to support buses, cycling, walking and road traffic.
As of August 2026, LTA said more than 90% of foundation works for both viaduct and tunnel sections had been completed, with excavation progressing along the 12.3-kilometre tunnel alignment.
The project also shows why underground engineering is difficult in an already-developed city.
Construction has to avoid or work around existing roads, utilities and operational MRT infrastructure.
The Utility Problem Below Ground
Cities contain buried power cables, water pipes, sewers, telecommunications ducts and other services.
If each utility digs separately, streets are repeatedly disrupted and underground space becomes chaotic.
URA therefore supports common-service tunnels and utility-specific ducts that consolidate multiple services and preserve spare capacity.
The idea is simple:
plan the underground before everyone arrives.
The National Infrastructure Plan
URA’s Infrastructure Planning Authority Group coordinates long-term infrastructure planning across agencies.
Through the National Infrastructure Plan process, infrastructure agencies submit 15-year plans for review and alignment with land-use plans.
This matters because underground conflicts can be extremely expensive to fix after construction starts.
Coordination has to happen before the tunnel-boring machine arrives.
MRT Stations Are Underground Town Centres
Many MRT stations now connect directly to malls, offices, homes and pedestrian networks.
URA encourages underground pedestrian links between commercial developments and rapid-transit stations, with barrier-free public circulation and activity-generating uses such as shops and food outlets.
That means underground space can become commercial space too.
The station becomes a street beneath the street.
The Downtown Pedestrian Network
Singapore’s central business districts already contain extensive underground pedestrian connections between stations, developments and commercial areas.
These routes create weather-protected movement in a hot and rainy climate.
The economic value comes from convenience.
If people can walk between offices, shops and stations without crossing major roads or getting soaked, the entire district becomes easier to use.
Deep Tunnel Sewerage: The Water City Under the City
Singapore’s Deep Tunnel Sewerage System carries used water by gravity through deep tunnels toward major reclamation plants.
That connects underground infrastructure directly to Crazy Rich Singapore | NEWater, Water Technology and the Value of Scarcity.
The sewer is not merely hidden waste infrastructure.
It is part of the national water-recycling loop.
Jurong Rock Caverns: Storage Inside the Earth
Singapore has also built underground rock caverns for industrial storage.
This frees surface land for other uses while placing suitable storage functions inside rock formations.
The principle is powerful:
Not every land use needs daylight.
If a function can operate safely underground, the surface can be reserved for uses that benefit more from access, visibility and public life.
Why Underground Space Helps Green the Surface
Moving infrastructure below ground can free surface space for parks, housing, streets and public activity.
This connects the underground city to Crazy Rich Singapore | Green Buildings, Smart Districts and Sustainable Real Estate.
Urban sustainability is not only about making buildings greener.
It is also about deciding which functions should disappear from view entirely.
Why Tunnelling Requires Metrology
A tunnel boring machine cannot be allowed to drift.
Engineers continuously measure alignment, ground movement, settlement and structural response.
That connects underground infrastructure to Crazy Rich Singapore | Precision Engineering, Metrology and the Machines Behind the Machines.
Deep infrastructure is giant engineering controlled by tiny measurements.
Why Underground Construction Is a Risk-Management Industry
Tunnels pass near buildings, roads, utilities and water-bearing ground.
That creates engineering and financial risk.
Teams use monitoring instruments, staged excavation, ground improvement and emergency procedures to reduce that risk.
The invisible city has to be built without damaging the visible one.
What Students Can Learn from Underground Singapore
Physics
Ground pressure, structural forces, ventilation and fluid behaviour all matter underground.
Mathematics
Surveying, alignment, geometry and settlement monitoring require precise calculations.
Geography
Geology and land scarcity determine where underground infrastructure is practical.
Engineering
Tunnels integrate civil, mechanical, electrical and safety systems.
Economics
Underground construction trades high upfront cost against long-term land and connectivity value.
Civics
Multi-agency planning shows why major infrastructure requires coordination over decades.
Ten Vocabulary Words for the Underground City
1. Tunnel boring machine
A large machine designed to excavate circular tunnels through soil or rock.
2. Geotechnical
Relating to the engineering behaviour of soil and rock.
3. Settlement
Downward movement of ground or structures caused by changes beneath the surface.
4. Utility duct
A dedicated underground route carrying pipes, cables or services.
5. Common services tunnel
A shared underground tunnel carrying multiple utility networks.
6. Interchange station
A station connecting two or more rail lines.
7. Excavation
Removal of soil or rock to create underground space.
8. Alignment
The planned horizontal and vertical path of a road, rail line or tunnel.
9. Cavern
A large underground space excavated in rock for storage or infrastructure.
10. Subterranean
Located beneath the ground.
Frequently Asked Questions
How long will the Cross Island Line be?
LTA says it will be more than 50 kilometres long and fully underground.
How long is the North–South Corridor tunnel section?
The tunnel section spans about 12.3 kilometres.
Why does Singapore use underground space?
To preserve scarce surface land, reduce environmental and traffic impacts, and create space for transport, utilities, storage and pedestrian networks.
Is underground infrastructure always better?
No. It is more expensive and technically complex, so it is used where long-term land, connectivity or environmental benefits justify the cost.
What other infrastructure is underground in Singapore?
Examples include MRT lines, the Deep Tunnel Sewerage System, pedestrian links, utilities and Jurong Rock Caverns.
Helpful Reading Across the Singapore Graph
- How Singapore Connects | MRT Signalling, Train Control and Platform Screen Doors
- How Singapore Connects | MRT Depots, Bus Depots and Overnight Maintenance
- Crazy Rich Singapore | NEWater, Water Technology and the Value of Scarcity
- Crazy Rich Singapore | Land Reclamation, Long Island and Engineered Geography
References and Current Sources
- Land Transport Authority, Cross Island Line.
- Land Transport Authority, North–South Corridor: Revised Completion Timeline, 17 September 2026.
- Urban Redevelopment Authority, An Underground of Possibilities, updated 27 July 2026.
- Urban Redevelopment Authority, Enhancing Underground Infrastructure, updated 10 July 2026.
Crazy Rich Singapore Digs Down
Land scarcity usually makes cities look upward.
Singapore also looks downward.
Did you know? One of Singapore’s richest urban resources is not land on the map at all—it is the three-dimensional space beneath the map.