Here's Why Los Angeles' Roads Get Ridiculously Slippery When It Rains

The recent rains in Southern California from Tropical Storm Hilary made for dangerous road conditions in much of the region. While a lot of Southern Californians still can’t drive when roads get wet, there are actual reasons why LA roads get so treacherous in slick conditions, Spectrum News explains.

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Data from a 2003 study done by UC Berkeley shows that fatal crashes on rainy days increased threefold, but only when those periods of rain followed dry spells that were longer than three weeks. The reason is the buildup of gunk on roads during these dry spells that cause roads to get more slippery when they’re wet.

When the weather is warm and sunny — like it is most of the time in Southern California — things like oil, grease, tire rubber, and dust accumulate on roads. As the days go on without any rain, all these substances build up enough to create a thin layer over road surfaces. The sun essentially bakes this gunk into the road.

Worse yet, the longer it goes without rain, the more build up accumulates. Before Tropical Storm Hilary, most of LA and the surrounding region hadn’t seen that much rain since the extremely wet winter at the beginning of 2023. That’s over half a year’s worth of build up on roads and freeways in the region.

When the rain finally hits, the water causes all the substances to rise to the surface of the roads, creating slippery conditions and unfortunately increasing crashes. Sadly, most people that live in the area won’t even take this into account the next time it rains, and the same song and dance of backed up freeways because of crashes or a car losing control will play out on freeways and roads all across Southern California.