Are California roads really all that much more slick after rain?

In CA you will often see in the news and in idle conversation warnings about slick roads when it rains. If you’re not a native, this is somewhat bemusing. Duh?

But wait! The natives say - in CA oil and gas build up on the roads making them much more dangerous than you are probably used to!

I don’t think anybody disputes the idea that oil+water is slick, but having lived in CA for over a decade now I really haven’t seen any evidence that CA roads are significantly more slick than anywhere else during rains due to this supposedly dangerous “oil build effect”.

Is there any objective data on this?

As a former motorcyclist who commuted over Highway 17 for twelve years, drove for a courier service for 14 years and drove a single unit beverage truck for six, yes, they are far more slippery on the first few rains.

I can’t imagine why California roads would be much more slick (at the onset of a rainstorm) than any other place which has experienced a similar dry spell; it’s just that many places in California can go for a very long time without getting cleaned by a good storm.

We have warnings and awareness about driving in the rain in NY/NJ too. Common sense, I think.

But I don’t really know whether these warnings are stronger than the ones on the west coast.

Right, so I think the crux of the matter is really if this effect continues to build in significance over time indefinitely or not.

Is six months without rain much more dangerous than a month, or is it a small effect?

The only question I got incorrect when I took the exam to get my driver’s license as a teenager in Connecticut was about when roads are slickest after it rains. So I think California is not unique in wanting its drivers to be aware of this fact.

Agree. However, the degree to which it is emphasized seems unique to me after having lived in Maryland, Pennsylvania, Florida, and New Jersey, and spent time just about every where else in the nation.

This. And also the majority of California residents live in places where it doesn’t rain very often, and there are a lot of people in California, meaning both that a broadcast warning will reach more ears and that a Californian who loses control of their car is more likely to hit another car.

Even if it seems excessive or obvious, warning tens of millions of people who don’t often drive in the rain to be careful can have a much bigger positive effect here than in other places (where the roads are just as slick in the first rain).

The commuter roads also have a lot more use than other jurisdictions. We have a lot more drivers, it is longer between rains and the commute roads are very heavily used. Hwy 17, that someone mentioned above also has a lot of serious curves in addition to all of that. And we drive too fast. 70 being the normal low on freeways.

I am always deeply amused seeing cars that have landed after launching themselves off more or less straight freeways during a light rain.

I would think the more significant effect is that after six dry months, more people will have forgotten how to drive in rain. It’s like snow in much of the UK - infrequent enough to be a lot more hazardous than it would be for those who are used to it.

“Slow down and give more space to other cars” isn’t that hard to remember, even for Californians. And on the first fall rain, (Once it rained in late August! Saw it myself.) radio DJs are saying it on the radio and folks are reminding each other, too. Driving in rain is significantly more difficult than driving in snow, and we normally get plenty of practice October through April.

Happens on rural country roads that curve a lot … the ones that lumber trucks use that is and happens every year after a long dry season.

I’ve been the passenger in a car that all of a sudden was on two wheels going around a corner and if she had of put on the brakes we would’ve had quite a ride down a long mountain.

Thank God she didn’t and barely missed the next car headed for us when the car went back down on all four tires.

Yes, they get slippery not sure about the interstate ones though.

This (more or less). California has a gazillion cars on the road and often long stretches between cleansing rain-showers. Gunk builds up quickly and is cleaned off infrequently.

Common wisdom has long held that it’s only at the beginning of the rainy season that you need to be extra careful, because the oil and grease leaked onto the roads during the dry season hasn’t been washed off yet.

OTOH, cars today generally don’t leak nearly as much oil and grease as they used to. If you look at historic images of heavily used streets and parking lots, the dark swath of leaked oil down the center of every lane is often starkly evident, and similarly for the grease smudge in the center of every parking spot. You don’t see that nearly so much today. So it could well be that the warnings about the increased danger of driving in an early rainstorm has become nothing more than a shibboleth.

But in those places the first rain of the season doesn’t inspire front page newspaper stories the way it does here. When I moved out here I was surprised at the number of accidents on the first day of rain. We get one set of people who drive too fast for conditions, another who drive too slow for conditions, and the result is chaos.

It is definitely very true that cars leak less gunk onto the roads than they used to (especially in the days before PCV valves replaced draft tubes), but on the other hand there’s a heck of a lot more traffic on the freeways in California than there used to be.

I agree and I think that there is another explanation for the slickness. It’s not oil. Most cars do not leak oil. What every single car and truck does leave on the road is rubber (in the form of very small dust like rubber particles) and it’s this that is being washed up and causing the slick conditions.

It’s just the first few rainstorms that are the issue. Not driving in rain per se.

California has a Mediterranean dry-summer wet-winter climate. Not only is this, world wide, a very rare climate (besides the west coast of N.America and the Med, there is only the central coast of Chile, the Cape of Good Hope and a small part of Australian coastline), we also have the harshest version in the world, in that it has the longest completely dry period of all Mediterranean climates.

Where I live, we average about 40" a year of rain, and usually all of it falls in five months. The rest of the time it is perfectly rainless. Not only are the roads accumulating gunk on them during this very long dry period, the storms tend to be days in length, and relatively violent. It’s not Maryland, is what I’m trying to say here.

I think the concept of rain being that seasonal - aside from when it’s cold and thus the rain is snow - is what is baffling to much of the rest of the country. I’ve lived in the Midwest all my life and we get rain year-round when it’s not too cold (and therefore falling as snow).

I think you’re right - people don’t realize that it just does not rain (in much of the state) between April and October, so by the time monsoon season hits, the roads have a pretty good accumulation of dirt and dust and oil and rubber. And soot - because for us, summer is fire season. Just add water to the mix and wheeeeeeee!

Also, the population of California has about doubled since 1970, and in my home town there are EXACTLY the same number of freeway lanes today as there were back then. So, LOTS of cars on the road.