How Underground Space Is Planned in Singapore

Singapore is short of land only if the city is imagined as a flat surface.

Below the roads, buildings and parks sits another planning layer: MRT tunnels, road tunnels, water pipelines, sewers, electricity infrastructure, pedestrian links, service reservoirs, utility corridors, basements and deep storage caverns.

Moving infrastructure underground can free surface space and reduce visual or environmental conflict. It also creates a new scarcity. Tunnels cannot pass through one another casually. foundations extend downward. groundwater and geology matter. maintenance access has to remain possible. a project built too early in the wrong place can block a better future alignment for decades.

Singapore therefore increasingly plans underground space as infrastructure in its own right. URA’s Infrastructure Planning Authority Group coordinates major network planning, the National Infrastructure Plan aligns agencies over a rolling 15-year horizon, and a Major Infrastructure Workflow coordinates delivery along shared corridors.

The deeper planning principle is: the underground cannot be treated as leftover space after surface buildings are designed. It has to be reserved, mapped and sequenced before competing systems occupy it.

Quick answer: what does Singapore put underground?

Linear infrastructure: rail, roads, water, sewage, electricity and utility lines.
Basement space: pedestrian links, retail, car parks, utility facilities and deeper infrastructure such as MRT stations and water-reclamation facilities.
Shared utility corridors: Common Services Tunnels and Utility Specific Ducts that consolidate infrastructure and preserve capacity for future lines.
Deep caverns: large spaces built in suitable rock, including the Jurong Rock Caverns and Mandai Underground Ammunition Facility.
Water infrastructure: facilities such as the Bidadari Underground Service Reservoir and Stamford Detention Tank.
Future possibilities: further storage, water, energy and other infrastructure subject to engineering, safety and economic feasibility.

1. Underground planning begins with a vertical city map

Surface planning asks which parcel is residential, industrial, road, park or railway.

Underground planning adds depth. A road may occupy the surface while an MRT tunnel passes below it, a sewer tunnel runs deeper still and piles from surrounding buildings occupy other parts of the same volume.

The planning problem is therefore three-dimensional. Two projects can look non-conflicting on a two-dimensional map and still collide underground.

2. The National Infrastructure Plan moves coordination upstream

URA’s current 2026 National Infrastructure Plan, or NIP, aligns land-development agencies, infrastructure agencies and utility licensees over a 15-year horizon.

Agencies submit their infrastructure plans annually for review. This creates a recurring opportunity to detect competing needs before individual projects are too advanced to move.

The NIP therefore acts as a shared future map rather than waiting for two agencies to discover a clash during excavation.

3. Fifteen years is long enough to see conflicts and short enough to keep updating

Infrastructure often takes many years to plan, fund, design and construct.

A short planning horizon would miss projects whose land and corridor requirements need protection long before construction. An entirely fixed multi-decade plan could become stale as technology and demand change.

The annual 15-year review gives Singapore a rolling window: future enough to safeguard space, current enough to revise assumptions repeatedly.

4. IPAG gives cross-agency infrastructure planning an institutional owner

URA formed the Infrastructure Planning Authority Group, or IPAG, to oversee master planning of major infrastructure network plans across the Infrastructure and Environment sector.

This solves a structural problem. Every agency understands its own network best, but no single utility agency naturally owns the empty underground space shared by all networks.

A coordinating authority is therefore needed to compare corridors, sequence projects and decide where co-location or safeguarding can reduce future conflict.

5. Linear infrastructure competes for the same corridors

Railways, road tunnels, water pipelines, sewers and electrical systems all prefer routes that are technically feasible and economically efficient.

Those routes often converge along the same transport and development corridors.

If each agency optimises independently, the first project can occupy the easiest depth and alignment while forcing every later project into deeper, longer or more expensive alternatives.

Underground planning therefore asks not only “Can this tunnel fit?” but “What future systems also need this corridor?”

6. Common Services Tunnels reduce repeated utility corridors

URA’s Master Plan 2025 materials identify Common Services Tunnels, or CSTs, as one strategy for consolidating multiple utilities underground.

Instead of placing every utility in a separate buried alignment that later requires its own excavation, shared tunnels can carry multiple services while preserving access for maintenance.

The value is larger than saving trench width. A maintained tunnel can reduce future road openings and make repair or replacement less disruptive to the surface city.

7. Utility Specific Ducts preserve spare capacity

URA also identifies Utility Specific Ducts as a way to consolidate lines and provide spare capacity for future infrastructure.

This is a simple but powerful future-proofing principle: installing usable underground capacity during one construction phase can be cheaper and less disruptive than reopening the corridor years later.

The city spends slightly more effort today to preserve a lower-friction option tomorrow.

8. Rail tunnels free surface land but create protection zones

Much of Singapore’s MRT network runs underground.

Putting rail below ground reduces surface severance and allows roads, buildings and public spaces to continue above. But underground rail structures then have to be protected from nearby excavation, piling, drilling, heavy equipment and development works.

LTA therefore regulates development within railway corridors and protection zones. Underground space is useful because multiple uses can stack vertically—but only if later construction does not damage the infrastructure already underneath.

9. Road tunnels solve surface congestion at a high underground cost

Road tunnels can move major traffic flows below the surface and release land or street space above.

They require large cross-sections, ventilation, emergency access, drainage, fire protection and long approach geometry.

A future road-tunnel corridor therefore has to be safeguarded well before construction so buildings, deep basements or other tunnels do not occupy the alignment irreversibly.

10. Sewers can go very deep because gravity creates value

Singapore’s Deep Tunnel Sewerage System uses deep tunnels to move used water over long distances toward major water-reclamation plants.

Deep alignment allows the network to use gravity and reduces the need for many surface treatment plants and pumping facilities.

The depth also reduces some competition with shallower infrastructure, but it increases geological, construction, access and maintenance complexity.

11. Basements form the shallowest large underground layer

Private and public developments use basements for parking, retail, pedestrian connections, plant rooms and services.

This shallow underground layer is often commercially valuable because it connects directly to buildings and streets.

It is also where conflicts with future rail tunnels, utility reserves and neighbouring foundations can begin. A deep basement decision made on one parcel therefore can affect infrastructure options outside that parcel.

12. Pedestrian links make underground space part of the public realm

Underground space is not only for machinery.

Pedestrian networks around MRT stations and major mixed-use districts allow people to cross roads, connect buildings and move through air-conditioned or weather-protected routes.

The planning challenge is legibility. A network of basement links can become highly convenient or deeply confusing depending on continuity, level changes, accessibility and wayfinding.

13. Deep caverns use geology as land supply

Where rock conditions are suitable, caverns can create large underground volumes for uses that do not require daylight or street frontage.

URA identifies the Mandai Underground Ammunition Facility and Jurong Rock Caverns as existing examples.

Jurong Rock Caverns demonstrate the land-saving logic particularly clearly: storage can be moved into deep rock while scarce surface land in an industrial area remains available for other productive uses.

14. Water infrastructure can also disappear beneath the city

URA’s current underground-space plan highlights facilities such as the Bidadari Underground Service Reservoir and Stamford Detention Tank.

Putting large water-management facilities underground allows the surface above or around them to serve other urban functions while the infrastructure continues performing a critical utility role.

This is a form of vertical land recycling: one geographic footprint performs more than one city job.

15. Not every infrastructure use belongs underground

Underground construction is expensive and technically demanding.

Fire safety, ventilation, waterproofing, emergency egress, groundwater, geology and maintenance access can make an underground solution much more complex than a surface facility.

The correct question is therefore not “Can Singapore put this underground?” but “Is the surface land saved worth the full lifecycle cost and risk of putting it underground?”

16. Underground fire safety changes the design problem

Smoke and heat behave differently in enclosed underground spaces, and occupants may have fewer intuitive escape routes.

Fire compartmentation, smoke control, detection, suppression, emergency ventilation and protected egress become central design requirements.

URA’s 2026 Master Plan material explicitly identifies fire safety as one of the technical challenges that must be overcome if Singapore is to expand the range of basement uses.

17. Groundwater makes every deep excavation part of a wider physical system

Excavating below ground can alter groundwater movement and affect adjacent soil or structures if poorly managed.

Deep infrastructure therefore requires geotechnical investigation, structural design and construction controls that understand the surrounding ground rather than only the final empty space being created.

The underground city is embedded in geology; it is not a set of hollow tubes floating independently beneath Singapore.

18. Mapping underground utilities reduces accidental disruption

Existing underground records are critical because contractors need to know where cables, pipelines, tunnels and structures lie before excavation begins.

URA’s July 2026 infrastructure-planning framework emphasises more accurate underground data and improved site-investigation workflows.

Better data reduces construction risk, utility strikes and service disruption while also helping planners identify where future infrastructure can still fit.

19. INPAC creates a digital coordination layer

URA’s Infrastructure Network Planning & Alignment Clearance platform, or INPAC, supports communications, consultations and planning among multiple agencies.

Digital coordination matters because the underground conflict often begins as an information conflict: one agency does not yet know another agency intends to use the same corridor five years later.

A shared planning platform allows potential clashes to become visible before construction drawings are locked.

20. The Major Infrastructure Workflow gives shared corridors a lead coordinator

URA introduced the Major Infrastructure Workflow in 2024 for major network projects.

Under the workflow, a Lead Implementing Agency can coordinate several infrastructure projects along the same corridor.

URA says this helps optimise underground space, reduce conflicts, safeguard space for future infrastructure and minimise repeated excavation and diversion works.

The institutional lesson is powerful: when several agencies share one corridor, somebody needs to own the integration problem rather than asking each agency to optimise independently.

21. Construction sequence can matter as much as final geometry

Two underground systems may fit geometrically in the final state and still be difficult to build in the wrong order.

A later tunnel may have to pass beneath a completed structure. Utility diversions may be required before station excavation. temporary access may need land that disappears once another project starts.

Infrastructure coordination therefore plans time as well as depth.

22. Spare capacity is a deliberate future option

Underground structures are expensive to reopen.

Where future demand is plausible, adding spare ducts, access space or expansion provisions during initial construction can preserve valuable options.

The cost must still be justified. But in a dense city, the future cost of finding that no corridor remains can be far larger than the cost of modest spare capacity built early.

23. Underground planning can release the surface for people

The most visible benefit of underground infrastructure is often what is no longer visible.

A utility facility below ground can leave room for a park. a rail line below a district can avoid a surface barrier. a common services tunnel can reduce repeated road excavation. an underground reservoir can preserve land above for other use.

The objective is not to hide infrastructure because infrastructure is unattractive. It is to assign scarce surface frontage to uses that benefit most from daylight, access and public presence.

24. A worked example: several agencies want the same street corridor

Imagine LTA needs a future transport tunnel, PUB needs a large water line and an electricity network needs additional capacity along one growing district.

If each project arrives independently, the first may occupy the easiest alignment and force the others into expensive diversion.

Under an upstream coordination model, the projects appear together in the infrastructure-planning horizon. agencies compare depth, sequencing and co-location. space can be safeguarded and a lead implementation approach selected where useful.

The result is not necessarily one giant tunnel. It is a coordinated decision made before accidental conflict becomes engineering fact.

25. A worked example: deep storage instead of surface storage

Suppose a strategic storage use requires large volume but little daylight or public frontage.

If geology, access, fire safety and economics support it, a cavern can move that volume into rock and free surface land for uses that benefit more from location above ground.

The city has not created more territory. It has increased the number of useful layers within the territory it already has.

26. Common misconceptions

Misconception: Underground space is empty until someone builds in it.
No. foundations, groundwater, utilities, protection zones and future safeguarded corridors already constrain much of the subsurface.

Misconception: Putting infrastructure underground always saves money.
No. it can save surface land and reduce some impacts while costing substantially more to construct, ventilate, waterproof, protect and maintain.

Misconception: Underground planning is mainly an MRT issue.
No. roads, water, sewage, electricity, storage, pedestrian networks and other infrastructure compete for the same three-dimensional city.

Misconception: Digital mapping removes the need for site investigation.
No. records improve planning, but actual subsurface conditions still need to be verified through appropriate investigation and engineering.

Misconception: Every spare underground volume should be developed.
No. future flexibility itself can be valuable; some space is best preserved until a stronger need and better information emerge.

27. The deeper idea: Singapore is learning to reserve volume, not only land

Traditional planning treats land as parcels on a map.

A dense mature city eventually discovers that the scarce resource is three-dimensional. The same street can carry people above ground, retail below ground, utilities in a shared corridor and a rail tunnel deeper beneath them. But every layer has to be compatible with the others.

Singapore’s newer infrastructure-planning architecture recognises that reality. The National Infrastructure Plan creates the forward view. IPAG supplies the coordinating institution. the Major Infrastructure Workflow aligns delivery. INPAC and better underground data improve the shared evidence base.

The city is no longer only deciding what owns each piece of surface land. It is deciding which future system deserves each part of the volume beneath it—and how to preserve enough empty volume for needs Singapore does not know yet.

How Underground Space Is Planned in Singapore: Rail, Roads, Utilities and Storage Beneath a Dense City