Crazy Rich Malaysia | SMART Tunnel, Flood Control and the Climate Resilience Economy begins with one of Kuala Lumpur’s strangest pieces of infrastructure: a road tunnel that can become a stormwater tunnel when the city needs protection more than it needs traffic.
Did you know the SMART system is built around a tunnel roughly 9.7 kilometres long and covers the Sungai Ampang and Sungai Klang catchments around some of central Kuala Lumpur’s most flood-sensitive areas? The operator says the SMART coverage area represents about 45% of Kuala Lumpur’s total flood-prone areas.
That makes “SMART Tunnel Malaysia”, “SMART Tunnel Kuala Lumpur”, “Kuala Lumpur flood tunnel”, “SMART highway”, “KL flood mitigation”, “stormwater tunnel Malaysia”, “Kuala Lumpur floods” and “climate resilience Malaysia” powerful search themes. But the richer story is not the tunnel.
It is the idea that infrastructure can have two jobs and switch between them when the city’s priorities change.
Crazy Rich Malaysia can be a motorway on Monday and a river on Tuesday.
Did You Know? SMART Means Stormwater Management and Road Tunnel
The acronym explains the concept.
SMART was created primarily to reduce recurring flooding in Kuala Lumpur’s city centre.
During design, engineers added a second use:
road traffic.
That created a rare dual-purpose system.
In normal conditions, motorists use the road section.
During major storms, traffic can be removed and the same tunnel becomes part of the flood-diversion system.
One expensive underground asset therefore performs two urban jobs:
- reduce road congestion; and
- protect the city from floodwater.
This is infrastructure utilisation at a very high level.
Why Kuala Lumpur Needed a Flood Diversion System
Kuala Lumpur grew around rivers.
That geography helped create the city.
It also created flood risk.
The SMART operator explains that a critical stretch of Sungai Klang near central Kuala Lumpur is constrained by river geometry and structures including the Jalan Tun Perak Bridge near Masjid Jamek.
During heavy rainfall, excessive flows can raise water levels enough to threaten surrounding low-lying areas.
The SMART concept reduces that pressure by diverting water before too much reaches the critical city-centre stretch.
The urban flood problem is therefore partly a capacity problem.
The river can carry only so much water through a constrained corridor.
SMART creates another route.
The System Starts with a Holding Pond
Floodwater does not simply enter the motorway tunnel directly from the street.
The SMART flood-mitigation system includes a holding pond, bypass tunnel and attenuation storage.
The system diverts excess flow from the Klang–Ampang river system toward storage before releasing water in a more controlled way downstream.
This is important because flood management is often about timing.
Rain may fall too quickly for the downstream river system to carry safely.
Temporary storage buys time.
Infrastructure transforms a sudden peak into a more manageable flow.
Flood control is therefore partly a problem of moving water and partly a problem of slowing time.
SMART Has Four Operational Modes
The tunnel does not simply switch between “road” and “flood”.
It operates through four modes that allow progressively stronger flood response.
Mode 1: Normal Traffic
When weather is fair or rainfall is minor, the motorway remains open and the tunnel performs its transport function.
Mode 2: Moderate Rain
When flow at the upper Klang–Ampang confluence reaches the operator’s stated moderate-rain threshold, excess water is diverted through the lower drains while the road tunnel can remain open.
Mode 3: Major Storm Warning
If a major storm is forecast and flows rise toward the higher threshold, traffic is evacuated from the motorway section.
The road is no longer treated primarily as transport infrastructure.
The system prepares it to become flood infrastructure.
Mode 4: Full Flood Diversion
If heavy rain continues, the road tunnel itself is used to carry floodwater.
This is the extraordinary moment when the design reveals itself fully.
A road becomes part of a stormwater channel.
Mode 2 Shows Why Dual Use Is More Than a Marketing Phrase
The cleverest part of SMART may not be the dramatic full closure.
It may be the middle condition.
During moderate storms, the lower drainage section can convey diverted water while road traffic remains open above.
That means the infrastructure can perform two functions simultaneously.
This increases asset utilisation.
Instead of choosing permanently between flood tunnel and road tunnel, the system shares the cross-section when conditions allow.
Multi-use infrastructure becomes economically attractive when the uses are compatible most of the time and one use can yield temporarily to the more urgent one during emergencies.
Mode 4 Is a Priority Algorithm Written in Concrete
When flood risk becomes severe enough, traffic loses priority.
That is the correct choice because the economic value of keeping cars moving is much smaller than the potential cost of uncontrolled flooding in the city centre.
The tunnel’s four-mode design therefore encodes a hierarchy:
- normal mobility when risk is low;
- partial flood management during moderate events;
- prepare for evacuation when risk rises; and
- protect the city when flood risk dominates.
That is systems engineering.
The city’s priorities are translated into operational logic before the emergency arrives.
Flood Gates Are the Physical Switch
SMART uses automated watertight flood-control gates around the motorway section.
During full flood operation, these gates help isolate and control the road tunnel so water can pass through safely.
This is an important engineering lesson.
Dual-use infrastructure needs a reliable switching mechanism.
A building can change rooms easily.
A flood tunnel cannot improvise.
The transition must be designed around:
- traffic evacuation;
- gate operation;
- monitoring;
- water levels;
- communications;
- emergency response; and
- the later cleaning and reopening process.
The switch between uses is itself a sophisticated system.
SCADA Makes the Tunnel Observable
SMART lists SCADA monitoring and surveillance among its core technical features.
SCADA—Supervisory Control and Data Acquisition—allows operators to monitor infrastructure and control equipment from central systems.
In a complex tunnel, operators need information about:
- traffic;
- air quality;
- equipment status;
- gates;
- water levels;
- ventilation;
- alarms; and
- unusual events.
A tunnel that cannot be observed cannot be managed intelligently.
Sensors turn buried infrastructure into a visible digital system.
Ventilation Is a Life-Safety System
Road tunnels need ventilation because vehicle exhaust and smoke can accumulate underground.
SMART includes ventilation and escape shafts, air-quality monitoring and specialised emergency equipment.
This is what good infrastructure often looks like:
the user experiences a simple road.
Behind the road sits a stack of invisible systems keeping the environment usable.
The motorway function therefore depends on:
- air quality;
- fire detection;
- communications;
- cross passages;
- emergency access;
- rescue vehicles; and
- continuous maintenance.
The road is only the interface.
The safety system is the product underneath it.
SMART Was Also Designed to Reduce Congestion
The motorway section gives motorists another route into and out of central Kuala Lumpur from the southern gateway.
The operator notes that a journey between the Jalan Istana Interchange and Kampung Pandan can take around four minutes through SMART compared with roughly ten to fifteen minutes on existing roads under the stated comparison.
That time saving creates everyday economic value.
Thousands of small time savings can accumulate across:
- commuting;
- business trips;
- deliveries;
- fuel consumption; and
- schedule reliability.
The tunnel therefore creates value even on days when no floodwater enters it.
The Tunnel Protects a High-Value Urban District
SMART’s coverage includes areas around Masjid Jamek and central Kuala Lumpur’s financial and commercial district.
This matters because flood risk is not measured only by water depth.
The same volume of water creates very different economic damage depending on what it floods.
Flooding a low-value empty field is not the same as flooding:
- commercial buildings;
- roads;
- electrical infrastructure;
- shops;
- offices;
- rail access;
- telecommunications; and
- the centre of a major capital city.
Protection becomes more valuable as the protected district becomes denser and more economically important.
A 2009 Storm Demonstrated the Importance—and Limits—of Coverage
SMART’s own FAQ explains that during a major Kuala Lumpur storm on 3 March 2009, the system diverted about 700,000 cubic metres of floodwater from the Klang–Ampang system.
Yet flooding still occurred around PWTC and Sentul because those areas were affected by different river catchments outside SMART’s designated coverage.
This is an important lesson.
Infrastructure has boundaries.
A successful flood tunnel cannot protect every drain, river and neighbourhood in the city.
SMART’s operator explicitly says its coverage represents around 45% of Kuala Lumpur’s flood-prone areas.
Good resilience planning begins by understanding what the system can do—and what remains outside it.
The 2021 Flood Event Showed the Scale of Emergency Diversion
During the severe December 2021 flood event, reports carried by the SMART operator described the system diverting around five million cubic metres of floodwater.
That figure helps make the tunnel understandable.
Five million cubic metres is not a normal transport quantity.
It is city-scale hydrology.
Large infrastructure earns its keep during rare events because rare events can produce enormous losses.
This is the economics of resilience:
most days look uneventful.
The value appears when the extreme day arrives.
Climate Change Raises the Value of Urban Flood Resilience
A warmer atmosphere can hold more moisture.
That can intensify heavy-rainfall risk in many regions even though local outcomes remain complex.
For a dense tropical city, this increases the strategic importance of:
- stormwater capacity;
- river management;
- retention ponds;
- drainage maintenance;
- flood forecasting;
- warning systems;
- land-use planning; and
- infrastructure capable of handling extremes beyond ordinary rainfall.
Climate resilience is therefore not a single tunnel.
It is a portfolio of systems designed around uncertainty.
Flood Forecasting Is Part of the Tunnel
Concrete cannot decide when to close a motorway.
Operators need data.
SMART’s operational modes depend on rainfall, river flow measurements and flood forecasting.
This makes weather and hydrological information part of infrastructure operations.
The tunnel system therefore combines:
- civil engineering;
- hydrology;
- meteorology;
- traffic control;
- software;
- sensors; and
- human decision-making.
The concrete is impressive.
The information layer tells the concrete when it is needed.
Maintenance Is What Makes Rare Emergency Infrastructure Trustworthy
Emergency infrastructure creates a maintenance paradox.
Some of its most important functions may be used rarely.
They still have to work immediately.
Flood gates cannot say:
“We have not been used recently, so please give us a day.”
Pumps, sensors, communications, ventilation and emergency vehicles need continuous inspection.
SMART’s management structure includes specialist mechanical, electrical, civil, highway and emergency-response teams.
Reliability is not a feature installed in 2007.
It is an outcome reproduced every day through maintenance.
Cleaning After Flood Diversion Is Part of the Design
When the road tunnel is used for full flood diversion, reopening is not simply a matter of draining the water.
The motorway must be inspected and cleaned.
Debris and sediment may need removal.
Electrical and mechanical systems need verification.
Road surfaces and safety systems must be checked.
The operator’s published Mode 4 procedure allows reopening within up to four days after closure, depending on conditions.
This reveals an overlooked principle of resilience.
Recovery time is part of system performance.
A resilient system does not merely survive.
It returns to useful operation quickly.
SMART Shows Why Infrastructure Should Sometimes Be Multi-Use
Urban land is expensive.
Underground construction is expensive.
That creates pressure to extract more usefulness from each major asset.
SMART’s dual-use logic is attractive because the two functions have different demand patterns.
Road capacity is useful every day.
Extreme flood capacity is critical only during specific storms.
Combining them makes an expensive tunnel productive under both ordinary and extraordinary conditions.
This idea is larger than SMART.
Resilient cities should constantly ask whether infrastructure can perform more than one compatible job.
But Multi-Use Infrastructure Requires Clear Priority Rules
Dual use is not automatically efficient.
It works only if the system can switch safely.
That means designers need to define:
- what triggers the transition;
- who has authority;
- how users are evacuated;
- how conflicting uses are isolated;
- how the asset is inspected afterward; and
- how the public knows what is happening.
Without priority logic, multi-use infrastructure can become multi-use confusion.
SMART succeeds conceptually because flood protection clearly outranks road traffic when the storm becomes severe enough.
SMART Is Also a Public Communication System
When a tunnel changes operating mode, motorists need to know.
The system uses public alerts, highway communications and operational notices to explain closures and reopening.
This may seem secondary to engineering.
It is not.
Infrastructure works through human behaviour.
A technically perfect evacuation plan fails if motorists do not understand the instruction.
The words-to-technology interface matters during emergencies too.
Clear communication converts engineering capacity into public safety.
Flood Resilience Protects Property Values Indirectly
People rarely pay a daily bill labelled “value of not being flooded”.
Yet reliable flood mitigation can protect:
- building interiors;
- electrical systems;
- inventory;
- business continuity;
- transport access;
- insurance conditions;
- tenant confidence; and
- the reputation of a commercial district.
Resilience therefore creates economic value partly through avoided loss.
This is difficult to celebrate because the successful outcome looks like nothing happened.
Nothing happening can be worth billions.
The SMART Tunnel Does Not Replace Ordinary Drainage
One of the most important facts in the operator’s FAQ is that SMART does not cover every part of Kuala Lumpur.
Flash floods can still occur because of:
- other river catchments;
- blocked drains;
- localised extreme rainfall;
- insufficient local drainage capacity;
- development patterns; and
- water entering places outside the tunnel’s catchment.
Big infrastructure does not remove the need for small infrastructure.
A city still needs functioning drains, culverts, detention ponds, river maintenance and local flood planning.
Resilience is layered.
No single project carries the entire city.
The Tunnel Is a Civil Engineering Education Machine
SMART compresses an extraordinary number of engineering disciplines into one project.
- tunnelling;
- hydrology;
- structural engineering;
- road engineering;
- mechanical systems;
- electrical systems;
- ventilation;
- traffic engineering;
- control systems;
- emergency planning; and
- operations management.
This makes the tunnel useful as a teaching case far beyond Malaysia.
The project demonstrates how engineers integrate systems whose failure modes interact.
The tunnel is not one machine.
It is a machine made of machines.
Kuala Lumpur and Singapore Face Different Water Problems
Kuala Lumpur’s SMART story centres on stormwater and flood diversion.
Singapore’s water story is shaped by land scarcity, water security, drainage, reservoirs, NEWater and engineered catchments.
Read Crazy Rich Singapore | NEWater, Water Technology and Value of Scarcity and Crazy Rich Singapore | Land Reclamation, Long Island and Engineered Geography.
Both cities reveal the same deeper principle.
Water is not only a natural resource.
In dense cities, water becomes an engineering problem.
Civilisation advances when it learns to move, store, clean and survive water intelligently.
What Students Can Learn from the SMART Tunnel
Physics
Water flow, pressure, ventilation and vehicle movement show fluid dynamics and mechanics operating at city scale.
Mathematics
Flow rates, storage volumes, probabilities and thresholds show why quantitative modelling matters in infrastructure.
Geography
River catchments and urban development explain why flood risk differs from neighbourhood to neighbourhood.
Engineering
Dual-use design shows how civil, mechanical, electrical and control systems can be integrated into one asset.
Economics
Avoided flood damage and travel-time savings show why infrastructure creates value even when no product is sold directly.
Ten Vocabulary Words for the Climate Resilience Economy
1. Stormwater
Rainwater flowing across land and urban surfaces after precipitation.
2. Catchment
An area of land from which water drains toward the same river, lake or drainage system.
3. Attenuation
The reduction or slowing of a peak flow, often by temporarily storing water.
4. Diversion
Redirecting flow away from its normal route toward another path.
5. Hydrology
The study of water movement, distribution and behaviour in natural and built environments.
6. SCADA
Supervisory Control and Data Acquisition: systems used to monitor and control infrastructure and industrial processes.
7. Resilience
The ability of a system to withstand disruption and recover useful function quickly.
8. Redundancy
Extra capacity or backup components designed to prevent one failure from collapsing the entire system.
9. Evacuation
The organised movement of people away from a place before or during danger.
10. Dual-use
Designed to perform two distinct functions under different operating conditions.
Frequently Asked Questions
What does SMART stand for?
SMART stands for Stormwater Management and Road Tunnel.
How long is the SMART Tunnel?
Published SMART material describes the overall tunnel as approximately 9.7 kilometres long.
Can cars use SMART while floodwater is flowing?
Under Mode 2, the lower drains can carry diverted stormwater while the motorway remains open. During more severe Mode 3 and Mode 4 operations, road traffic is evacuated or the tunnel is closed so floodwater can use more of the system.
Does SMART stop every Kuala Lumpur flood?
No. SMART’s operator says the system covers the Sungai Ampang and Sungai Klang catchments and around 45% of Kuala Lumpur’s flood-prone areas. Floods caused by other catchments or local drainage problems can still occur.
Why is SMART economically valuable?
It creates everyday transport benefits while also reducing the risk of high-cost flood damage to important parts of central Kuala Lumpur.
Helpful Reading Across the Singapore Graph
- Crazy Rich Malaysia | MRT, LRT and the Kuala Lumpur Urban Transit Economy
- Crazy Rich Malaysia | Solar Power, Renewable Energy and the Grid Transition Economy
- Crazy Rich Singapore | NEWater, Water Technology and Value of Scarcity
- Crazy Rich Singapore | Land Reclamation, Long Island and Engineered Geography
References and Current Sources
- SMART Motorway Tunnel, What Is SMART?, accessed October 2026.
- SMART Motorway Tunnel, Operational Modes, accessed October 2026.
- SMART Motorway Tunnel, Unique Features, accessed October 2026.
- SMART Motorway Tunnel, SMART Coverage Area, accessed October 2026.
- SMART Motorway Tunnel, Frequently Asked Questions, accessed October 2026.
Crazy Rich Malaysia Gives One Tunnel Two Lives
On ordinary days, people drive through it.
On dangerous days, water does.
The same underground space serves mobility and resilience because the system knows which purpose matters more at each moment.
Did you know? Sometimes the richest infrastructure is not the one built for the biggest number of normal days. It is the one clever enough to become something else on the day the city needs it most.