Images of hurricane Ida’s passage across the U.S. show a staggering number of vehicle rescues. Particularly in Louisiana, New Jersey and New York, motorists got in trouble by driving into flooded roads. “You could see them drive in and the car stopped and their lights went out,” another newspaper quoted an eyewitness. Countless times, first responders had to extract drivers from flooded cars, some alive, some not.
For years, the National Weather Service (NWS) has been running a campaign titled “Turn Around Don’t Drown”. After disasters like Ida, we’re used to reading about anonymous death tolls from drowning. But the NWS website makes a more direct point by stating that more than half of the casualties are people who drove into flooded areas.
Modern cars have a very low ground clearance. Depending on model year, the Toyota Camry has 6 inches between the road surface and where the car’s body starts. Ford Focus, 6.5 inches. Honda Civic, 6.9 inches. Ground clearance is higher in SUV’s and pickup trucks but can convey a false sense of security. It still doesn’t make them flood-safe. As an advertisement says, the Subaru Outback clears “a generous 8.7 inches”. Ford F-150, 9.4 inches. Dodge Ram, 8.7 inches. An average men’s shoe wouldn’t fit underneath, held upright.
Compare this tiny gap to the physical properties of water. One cubic foot of water weighs a hefty 63 pounds. The average footprint of a car is 45 square feet. A roadway flooded 10 inches deep may look quite innocent. But the car driven into it will displace a 37 cubic feet body of water that weighs more than 2,300 pounds. Most cars begin to float at that level. For trucks and SUV’s, the trouble starts near 12 inches of water. A floated vehicle is a very bad boat. Turn the steering wheel all you want, hit the gas, hit the brakes — nothing is working anymore. Electrical systems cut out after a few moments. All this happens even sooner when the floodwater is moving. Those 2,300 pounds underneath the car have tremendous pushing power. The car will drift toward the nearest ditch or ravine, and overturn. Could you get the windows down without electrical power?
All this doesn’t make it safer to drive on, say, just 4 inches of floodwater. You can’t see what’s lurking beneath. It could be a 10-foot deep collapse hole. Don’t drive into flooded roadways.
Rudi Kiefer, Ph.D., is a professor emeritus of physical science at Brenau University His column appears Sundays and at gainesvilletimes.com.