askST: Is it safe to drive through a flood?

A car seen partially submerged in flood waters at the junction of Pasir Ris Drive 12 and Tampines Avenue 10, on Aug 20, 2021.
A car seen partially submerged in flood waters at the junction of Pasir Ris Drive 12 and Tampines Avenue 10, on Aug 20, 2021.ST PHOTO: KEVIN LIM

SINGAPORE - An early morning downpour on Friday (Aug 20) caused several roads here to be flooded.

The Straits Times' transport and motoring correspondent Christopher Tan answers some questions on driving through flood waters.

Q: How safe is it to drive on a flooded road?

A: It is not a good idea to drive through a flooded road. But if you must, consider the depth of the water and the height of the vehicle you are driving. These two factors determine how likely water will get into the car.

A full-size sports utility vehicle (SUV) like a Land Rover Defender is much taller than say, a sports car.

The bottom of the doors on a typical family car are slightly higher than the top of kerbs on major roads. To be absolutely certain that water will not enter the cabin through the car's seals and drain holes, you can continue to drive if the kerbs are not fully submerged.

Q: What are the other risks of driving in a flood?

A: If you continue to drive when the kerbs are submerged, you may not know where the road boundaries are if you are in an unfamiliar location. You could mount a kerb and get stuck, or worse, end up in a flooded drain.

Another thing to consider is that when a vehicle's wheels are submerged, the brakes may not operate optimally.

There is also the risk of water entering the air intake. This will cause considerable damage to the engine. It will also stall.

If water enters the exhaust system, it might damage the catalyctic converter, which is costly to replace.

Q: What if I am driving an electric car?

A: Electric vehicles (EVs) can tolerate higher water levels because they do not have an air intake or an exhaust. But the risk of water entering the vehicle and damaging the cabin and sensitive electronic components is still present.

The higher the water level, and the longer a vehicle remains on a submerged road, the higher the risk.

If the water level is high enough, it might even come into contact with a vehicle's electronic control units (ECUs or computers which control various functions).

Again, this will cause considerable damage, and could cause the vehicle to stall. Both EVs and combustion-engine cars have ECUs.

Q: If I decide to drive on, are there things I should do differently?

A: When driving on a submerged road, proceed with a gentle and steady throttle. In other words, keep a slow and steady pace.

Do not lift your foot off or apply the brakes midway. This is to minimise turbulence and backflow, which might cause water intake.

You might want to follow a bigger, taller vehicle - like a bus or a truck - just to be sure you are on the right track.

If you are in a manual transmission car, stay in the second gear. If you in an automatic with an option to engage a lower gear, do likewise.

Go slowly, since braking and handling will be compromised on a flooded road.

After you have cleared the flooded area, apply the brakes gently for a minute or two to rid them of moisture.


Police pushing a minibus away after flood waters receded at the junction of Pasir Ris Drive 12 and Tampines Avenue 10, on Aug 20, 2021. ST PHOTO: KEVIN LIM

Q: What should I do if my car stalls in a flood?

A: If this happens, it is likely that water has entered the engine air intake. Do not restart the car, as this might cause further damage.

If the vehicle's main ECU is damaged, you will also not be able to restart it.

Switch on the hazard lights, and phone for help.

Even though you will get wet, it is safest to leave your stalled vehicle and get to higher ground. The water could continue to rise, and it might be difficult to open the door once the vehicle is half-submerged.