Driving through floodwater? Here’s how little it takes to float your car

You’ve reached a flooded road, the water looks shallow, and the detour is long. Driving through floodwater is the leading cause of flood deaths in Queensland, and float testing used by the Victoria State Emergency Service puts a small car’s limit at 15cm. What you can see from the driver’s seat tells you almost nothing.

How deep does water need to be before your car floats?

A small car floats in 15cm of water, which VICSES points out is roughly the height of an average pen. The number comes from tank testing on real vehicles by the UNSW Water Research Laboratory, done for the VICSES 15 to Float campaign, with the water moving at 3.6km/h. That is slower than you walk.

Weight buys far less than most drivers assume. These are the three float points from that testing, all measured at the same 3.6km/h flow speed, as published by VICSES.

Vehicle	Weight	Floats in	Flow speed
Small car	1.05 tonnes	15cm	3.6km/h
Mid-sized car	1.5 tonnes	30cm	3.6km/h
Four-wheel drive	2.5 tonnes	45cm	3.6km/h

A 2.5-tonne four-wheel drive only gains you 30cm of depth over a small hatchback, and that is the whole advantage. It is not much, and the numbers suggest drivers of big vehicles spend it. VICSES says deaths in four-wheel drives have climbed sharply across the past 15 years, and that almost 10 per cent of the requests for help it has taken since September 2016 involved a vehicle in water. In recent times it has answered more than 100 callouts to cars stuck in water.

Why can’t you judge the depth from the driver’s seat?

Because the two things that decide the outcome, depth and how fast the water is moving, are both hidden under a flat brown surface. Get Ready Queensland warns that as little as 15cm can cost a car its grip and carry it off the road, and that the steering, engine and electrics can all fail in water shallower than that.

The NSW SES asks drivers to assume every flooded road is dangerous, however calm it looks, and to be especially careful at night, when the depth is close to impossible to read. Its list of the reasons people talk themselves into it is short and familiar: faith in the vehicle, knowing the road, it being the route you always take, and watching someone else get through. Get Ready Queensland says research suggests many drivers overrate what their car can handle in water.

Driving into floodwater remains the number one cause of flood-related deaths in Queensland.

Rhys Newton, disaster coordinator, Cairns Regional Council, speaking to ABC News

Being wrong costs more the further you are from help, which is worth remembering when you’re driving on remote roads where a causeway can appear with no warning. Across a fortnight spanning the end of December 2025 and the first week of January 2026, Queensland crews dealt with more than half a dozen stranded vehicles, ABC News reported. One father and daughter escaped their car and then walked 13km for help. At Normanton, a man in his 70s was pulled dead from a car under water.

How should you drive in heavy rain?

Slow down, turn your headlights on, and treat the whole trip as the decision rather than the crossing at the end of it. The NSW SES asks you to look at the forecast before you leave, work out a second route in advance, and use the Live Traffic site to see which roads are shut. During flooding, travel only if the trip genuinely cannot wait. If you’re already somewhere safe, the advice is to stay there.

When visibility drops, the gap in front of you is the only thing you still control. Leave more of it. A wet surface stretches out your stopping distance, and spray off a truck can blank your windscreen for a second or two at a time. That is worse in the bush, so read up on sharing the road with road trains before storm season if you’re heading inland. If you can’t see, pull over well clear of the traffic lane and tell whoever is expecting you that you’ll be late, rather than press on.

Storms bring down more than water. The NSW SES says to assume any powerline on the ground is still live, and to keep 8 metres, about two car lengths, between you and it. That applies to the car as much as to you.

What should you do if your car stalls in floodwater?

Get above the water while you still can, because water in the electrics can leave your windows and doors dead. If rising flash floodwater traps you, the NSW SES says to shelter wherever is safest at that moment, which might be the cabin, the roof or ground above the car, to keep climbing as the level rises, and to call Triple Zero (000). For flood and storm help in NSW that is not life-threatening, the number is 132 500.

• Decide straight away whether you can open a door or a window, and do it before the electrics quit.
• Leave the car if you can reach higher ground on foot without stepping into moving water.
• If you can’t, climb onto the roof rather than stay in a filling cabin.
• Call Triple Zero and give your location as precisely as you can.
• Stay visible, and stay out of the current while you wait.

Then there is the bill. Queensland Police say the survivors still take a heavy financial hit, because the moment you drive in, your insurance is void, and an infringement for driving without due care and attention runs to $667, ABC News reports. Rescues also pull volunteers into the water behind you, which is why VICSES frames a stranded car as a risk to its crews and other responders, not just to the people inside it.

The way out of all this is to decide before you’re standing at the edge of it. Griffith University psychology professor Kyra Hamilton, who has written at least seven papers on why drivers enter floodwater, told ABC News to “make those detailed plans in your mind before the situation occurs.” Best for storm season is a rule you set at home, which is that a flooded road means turning around, every time. Jonathon Blackley, a swift water rescue technician with the Queensland Fire Department, puts the alternative plainly in the same report: sit the delay out, let the level drop, and satisfy yourself the surface underneath will carry a car before you go anywhere.