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VERIFY: Are roads really more slippery directly after it rains?

As KING 5 Meteorologist Rich Marriott explains, when it rains it forces fluids, like oil from cars, to the top making the roads very slippery right off the bat.

SEATTLE — Black ice is one thing to make a road slippery, but what about plain old rain? Is it really more slippery right when it comes down?

The answer is pretty simple: Yes, because oil and water don't mix. 

Longtime KING 5 Meteorologist Rich Marriott earned his undergraduate degree in physics and explained it succinctly.

"Cars on the roads leak fluids, oil being one of the primary fluids," said Marriott. "So, any water will tend to float the oil to the top, just like in salad dressing. So, as soon as you have water on the roads, that floats oil up and it becomes immediately very slippery."

Until the oil and dirt get washed away, the pavement will be slippery. That can happen in a matter of minutes during a downpour, according to Marriott. But, it's actually worse if it's simply drizzling, especially after a long dry spell. 

"In that case, it's going to stay slippery a lot longer," said Marriott. "You just think about it whenever you try to run something off with water. If you're doing a very slow pace, it takes much longer to get it rinsed off."

An examination of the first "wet day" of each of the last five years in Washington revealed that on those days, the Washington State Patrol responded to far more collisions than the previous day. The only outlier is 2020, whose smaller numbers are based on the stay-at-home order of the pandemic, resulting in far fewer cars on the road.

That’s anecdotal, perhaps, but it jives with the physics of oil and water – which allow us to verify: Yes, roads are more slippery, right when it rains or snows. 

So, make sure to slow down when it does.