By on May 13, 2019

Image: Mazda

It may not be a bombshell report that leaves mouths agape, but it reinforces an age-old bit of driving wisdom: when it starts to rain, slow down and leave a greater distance between you and the car in front.

A new study reveals just how much precipitation plays a role in increasinging the likelihood of a fatal crash. Even in weather docile enough to simply dampen one’s hair, death stalks the roadways like a vulture seeking out scraps of rancid meat.

The study, published in the Bulletin of the American Meteorological Society and first reported on by the , shows precipitation of all types increases deadly crash risk by 24 percent. In reaching their conclusion, researchers at the North Carolina Institute for Climate Studies probed 125,012 fatal car crashes in the continental U.S. from 2006 to 2011.

This study went beyond the sometimes vague police reports, analyzing the exact precipitation rate at the place and time of the crash using weather radar. While most drivers cut their speed sharply when it starts raining heavily, sometimes just for visibility reasons, the team was surprised to see just how deadly light rain is.

Just driving in light rain — “We’re talking a drizzle, just at the point where you might consider taking an umbrella out,” according to study lead author Scott Stevens — increased the chance of a fatal crash by 27 percent.

The most dangerous time to be driving in any rain, even drizzle, is just after the droplets start to fall. That rain mixes with oil, grease, and other residue on the road surface to make it extra slick, catching motorists off guard. After a sustained rainfall, most of that residue washes away, improving stopping distances. Thus, a road which has just seen a sprinkle can yield worse stopping times than a significantly wetter road that’s been soaked for hours.

Heavy rain, of course, can lead to hydroplaning, endangering even those who aren’t diving for an off-ramp. The visibility issue really comes into play, too. With the road ahead obscured and braking distances lengthened, no longer can drivers depend on the three-second rule.

Moderate rain, Stevens said, boosts the chance of a fatal crash by 73 percent. In heavy rain? It’s two-and-a-half times greater.

Population density also plays a role in the rate of fatal crashes. In heavily congested areas, most drivers aren’t going fast enough to die behind the wheel after something goes awry, even though their vehicle will sustain damage. The study showed that the Northern Rockies and Upper Midwest are the riskiest places to drive when the weather gets bad.

[Image: Mazda]

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43 Comments on “Even the Smallest Amount of Rain Sends Crashes Soaring, Study Finds...”


  • avatar
    newenthusiast

    This all makes sense of course, but I was unaware that even a brief drizzle could have THAT much effect (27%).

    Knowledge is power, so in the future, I’ll be adjusting my driving in wet conditions.

    • 0 avatar
      SunnyvaleCA

      Out here in silicon valley we have a no-rain season that lasts from May through October. The first rain in November, even if just a very light drizzle, mixes with 6 months of oil and grime sitting on the road surface. So even if visibility is fine and there’s no danger of hydroplaning, you are suddenly driving on a surface that is unexpectedly slippery.

      Also remember that there are new drivers on the road that already have 6 months of driving experience (so, some skill and confidence) WHO HAVE NEVER DRIVEN IN THE RAIN. In parts of the country with frequent rains, those first-time rain drivers only have a month of experience, so they are still (hopefully) more cautious generally.

      • 0 avatar
        ScarecrowRepair

        I saw a very interesting and even funny illustration of that many years ago. Major intersection, three left turn lanes. Guy in the middle left turn lane had some kind of muscle car, kept revving his engine as if to encourage the light to change. When it did, EVERYBODY sat still except for Mr MuscleHead, who jumped on it, spun around in the intersection, stopped, and crept away oh-so-slowly. It was amazing how everybody else knew what he was going to do. I’m sure most of us hoped Mr MuscleHead remembered the lesson next fall.

    • 0 avatar
      slavuta

      Its written in your owners manual, and driver manual. Take a look

  • avatar
    theflyersfan

    It doesn’t help that there are still too many drivers who don’t know where their headlight switch is located and uses it when they turn on their wipers. Visibility is everything in rain!
    We all have our commutes of misery the second something falls from the sky – and the LA Basin is legendary for acting like a few drops of rain = a blinding snowstorm on the roads – and it seems that more than a few of the TTAC faithful is from the Queen City area (not Charlotte) – so why in the bloody, raging, stinking hell does everyone lose their minds heading downhill on The Cut in the Hill??? Every single time a little rain falls, you might as well add an hour coming in from Northern Kentucky because of some mouth-breather re-arranging their fenders into someone else’s because they lost all sense and ability to gauge distances in the rain.
    Take it easy folks. You’ll get to where you’re going. Your tires aren’t going to defy the laws of physics, and regardless of what the tire commercials say, no tire is going to let you go through a standing pond at 70 mph and not have some drama!

    • 0 avatar
      FerrariLaFerrariFace

      When I grew up around there, we used to call that spot “dead man’s curve”. Apparently it still holds true.

    • 0 avatar
      theflyersfan

      https://en.wikipedia.org/wiki/Cut-in-the-Hill

      A little background about one dangerous road, especially in any kind of weather…

      • 0 avatar
        ScarecrowRepair

        370 feet in 4 miles is steep? That’s only 1.7%! Around here we have 3 mile grade which is signed for 6%, and the straights are only barely straight.

        • 0 avatar
          theflyersfan

          Part of it is the environment it’s in. I-75 is THICK with semi traffic, Northern Kentucky’s Cincinnati suburbs have exploded in population and there’s two main ways into Downtown Cincinnati, and points north in Ohio – The Cut in the Hill and I-471. The trucks stay on 71/75 through The Cut and on a worn out, narrow-laned, dangerous Brent Spence Bridge.
          There are some links at the bottom of the Wikipedia page to check out, including pictures of what it looked like before the reconstruction. It’s a little safer now, but with the increased traffic, heavy semi traffic, and overall cluelessness of the drivers, it’s still a white knuckle trip in any kind of weather.
          And I question those drop numbers (not from you, but from the website) – most of the drop is in the last mile where you get a jaw-dropping view of the Cincinnati skyline (especially at night – you make the first left turn to start the real descent and BAM, there’s the skyline) and doesn’t level out until maybe 1/2 a mile from the river and bridge.
          And uphill, even though it’s signed no trucks in the left two lanes…there’s always a semi going 25mph in one of the left two lanes! And it’s a long slog uphill!
          I’ve driven on some of those mountain grades out west and even in places where you might not think of it like in West Virginia (I-77 near Virginia comes to mind). But in an urban environment, with the sheer number of wrecks and fatalities, The Cut in the Hill rises near the top.

          • 0 avatar
            ScarecrowRepair

            I assume it got its reputation from something, but ….

            Three mile grade is on I-80 between Tahoe and the SF Bay Area, full of tired nuts racing to be first up the mountain Friday night, and tired and drunk nuts Sunday who’ve waited til the last minute to start for home. They just completed a truck lane, but before that, it was two lanes for three miles, 30mph trucks and RVs in the fast lane trying to pass 25mph trucks and RVs in the slow lane; rain, sun, snow didn’t matter. The new climbing truck lane will help some, but not enough to get me on that road Friday night or Sunday afternoon.

    • 0 avatar
      roverv8i

      My 2002 Grand Cherokee had automatic lights and included a setting that you could select in the settings menu in the overhead console that would turn the lights on for you when you turned on the wipers. Not when you hit mist of course. Any car that has automatic lights should have this on my opinion. In the Jeep you had to make the selection so I’m sure the majority of people that can’t be bothered to read the owners manual or look through the settings menus did not know they could do that. As we know you are always encountering people that should have there lights on and don’t because they have some sort of affliction that keeps them from putting their lights on automatic and in some cases ( lots of Toyota products ) you can defeat the daytime run lights so don’t even have them on. Regardless of whether you are pro or negative daytime run lights I think we can all agree that all cars should have their lights on or all off as when most are on it is hard to see those few outliers.

      • 0 avatar
        gomez

        My CR-V has a similar feature; the headlights automatically turn on if the wiper switch is engaged for 60 seconds. It’s a setting that must be enabled through the infotainment system and is not enabled by default, so most probably don’t know it exists.

        I think the widespread use of DRLs has made the problem worse. People think that because they have DRLs illuminated, they can be seen in bad weather. What people fail to realize is that their taillights are NOT illuminated.

        • 0 avatar
          theflyersfan

          DRLs and illuminated instruments/digital/virtual dashboards. If you don’t look for the little green “headlights are on” dash light, sometimes you’ll never know, especially in a bright city environment.
          Where’s the enforcement on light usage? If it’s 8:15 at night, and the sun is really low on the horizon, you need to be seen when driving. That to me is far more dangerous than 8 over the limit.
          And to add to @Garrett’s post, one of the most dangerous things I’ve seen on the interstate in some time happened last week. There’s a light drizzle after a fairly heavy rain and it’s getting dark while I head down I-71. The roads are wet, but in no way under water. Maybe a medium speed setting on the delay wipers. Nissan Rogue, left lane, lights off, going 35 mph on the freeway!!! If you’re that scared (or clueless) about driving at night on a wet highway in a light mist, US-42 follows I-71 and would be a lot safer for you!!! Not all speed kills – speed differential kills as well.

          • 0 avatar
            tankinbeans

            Throw improper usage of high beams as an issue, especially when it’s raining.

            Halo city.

  • avatar
    FreedMike

    I don’t know about crashes, but here in Denver, a brief rainstorm is enough to make I-25 into the a “millions of people fleeing the cities before the meteor hits” scene from “Deep Impact.”

    Then again, hills and curves do that too.

  • avatar
    Garrett

    A huge part of the problem is having timid drivers – people that are scared of driving in less than optimal conditions, who panic brake when it’s unnecessary, and who create moving chicanes on the freeways.

    Even in dry conditions, an unsure driver is as bad as someone on their cellphone or shaving behind the wheel.

    • 0 avatar
      James2

      This would probably describe 90-percent of the drivers here in HNL. Just enough rain to darken the surface-of-the-Moon pavement causes IMMEDIATE, Mommy, I’m scared backups. Literally and figuratively “just add water”.

      The last time this phenomenon happened, it was one of the last straws that broke this camel’s back and I changed jobs so I could walk to work. What was normally a 20-minute commute took three times as long, with no accidents or stalls that would normally cause a backup in dry conditions. And of course the “traffic engineers” are sitting in their offices, watching all of this virtual chaos on their big screens, and are probably laughing their useless asses off.

      What, us, adjust the signal timing or something? Surely, you jest.

    • 0 avatar
      Lorenzo

      No, it’s not the timid drivers, it’s the aggressive drivers who don’t adjust for conditions at all and endanger themselves and others. I saw a lot of them driving that way in the snow in Massachusetts, and when I moved to southern California, I discovered their “cousins” driving the same way in the rain, and even the fog.

  • avatar
    NeilM

    For quite a few years now I’ve been selecting my tires primarily based on superior wet performance, mostly based on published testing by Tire Rack.

    Most mid-range and better tires have enough dry grip that, unless you’re driving in “arrest me now” mode, they’re going to be good enough. But better wet grip can easily make the difference between kissing the guardrail or ramming the car in front, or not.

    This is one of the few basic characteristics of a car where the owner’s decisions can really make a difference.

    • 0 avatar
      gtem

      I agree Neil. My Civic came from the factory with Firestone Affinity “Fuel Fighter” tires that had comically horrible grip in the rain, surprising that that Honda spec’d that out in the first place. Likewise my parents’ 2007 Fit had horrible wet traction in the wet on the original factory tires. I’ve grown fond of General’s Altimax RT43 as a solid performer all around, maybe a tad louder and less efficient that some other all seasons, but with fantastic wet grip.

    • 0 avatar
      Scoutdude

      Agreed wet performance is the primary aspect I look at when choosing tires for most of my vehicles. I do live in the PNW so we have a lot of days with wet roads.

  • avatar
    EGSE

    Was pleasantly surprised that the article points out how hazardous the first light rain can be after an extended dry spell. I’m in a semi-rural area with lots of high-speed roads that are nevertheless heavily traveled (lots of pass-through commuter traffic to the D.C. burbs). In the first hour of a light rain or drizzle the dispatch radio wouldn’t shut up. At the station we’d sometimes “clean house” using whatever would roll…utility…brush truck…chief’s car…to get to crashes and stabilize the scene until an ambo could free up for transport. It really is that bad.

    • 0 avatar
      Scoutdude

      One thing I’ve noticed is that this problem has been dramatically reduced over time. Fact is cars just don’t leak fluids as frequently and as much as they used to, so there is much less oil on the road to cause the issue. You also see it on roads where there is not a black stripe of oil down the middle of the lane nor big spots after a bump/dip in the road that shake that small drop off.

      Take a look at these pictures from the 50’s when road draft tubes were still the norm. http://www.infomercantile.com/blog/labels/freeway.html It did get better in the 70’s with the PVC becoming the norm, but cars then were still using cork gaskets on tin covers meant a lot cars leaked and there was a general expectation that an older car would leak at least a little.

      • 0 avatar
        EGSE

        “a black stripe of oil down the middle of the lane nor big spots after a bump/dip in the road that shake that small drop off.”

        I used to ride motorcycles. It was understood you avoided riding in the center of the lane for this reason.

  • avatar
    ToddAtlasF1

    I’ve lived in Central Virginia hell, where the two seasons can be described as hot & wet and cold & wet. Rain might cause a small uptick in accidents there. I’ve also livid in a desert where lots of vehicles on the road were unmaintained. Some years it barely rained at all. When it did, the combination of vehicles that leaked oil and coolant, had bald tires, and had dried out wiper blades with drivers who had insufficient wet road experience made for horrific rainy day commutes.

  • avatar
    vvk

    Gotta pay for all the cheap Chinese and Korean tires being dumped on the US market. There is no free lunch.

    • 0 avatar
      gtem

      It’s both that and around here at least, no mandatory inspections (which I’m actually kind of thankful for on the one hand) lead to people driving around on some critically bald tires.

    • 0 avatar
      Scoutdude

      It truly amazes me what kinds of tires people will drive on. Just yesterday I was next to a fairly new Audi and the RF was just about ready to show some tire cords.

  • avatar
    tankinbeans

    I’m amazed at the amount of tailgating through all manner of weather; sleet, snow, rain, downpours, dry weather, and everything in between. This past winter I was cruising along in the right lane at just under the posted limit because the roads were less than stellar and warranted caution. Somebody at the front of the left lane conga line hit his brakes and everyone slammed on their’s. A nice little sin-wave started and I was worried that at least one car was going to slingshot out into my line.

    Fun times.

  • avatar
    MiataReallyIsTheAnswer

    The problem is not the rain, it’s the complete and total idiots driving 75% of the other vehicles on the road.

    It can be so simple to drive swiftly and efficiently in the rain—-

    -Have decent tires
    -Turn your effing lights on in your gray car in the rain at dusk
    -Pay attention
    -Observe the “left lane is for passing traffic” rule

    That’s it, it’s really that simple.

    • 0 avatar
      slavuta

      Most people probably don’t even know their tire condition

      • 0 avatar
        Scoutdude

        Yup and when it is time to buy tires the cheapest ones that are black and round is good enough. I find it particularly bad and not that uncommon to find the cheapest and/or baldest tires on expensive cars that are just a few years old.

  • avatar
    slavuta

    SHOCKING!

    haha

    All this is written in Driver Manuals and even car owner manuals. Just was reading days ago Toyota owner manual – bam! – it is there. Danger! Driving when rain just started – slow down. Yep, its in the owners manual

  • avatar
    geozinger

    Yes, this would seem like common sense, but very few people exhibit it.

    One of my pet peeves are the folks who use driving lights or fog lights in traffic in the rain. All the extra lighting just creates more glare than if they weren’t being used. I can see the point in using them only dimly lit or country roads, but in city traffic, they don’t help.

  • avatar
    Tele Vision

    Regardless of tire quality and wear most of us have about a palm’s width of with the road in any weather and at any speed. That truism has helped me through 35 Alberta Winters and many rain storms without a crash or an accidental off ( I’ve left the highway to avoid herds of deer and elk but, as I build roads for a living, I know that they’re designed for controlled excursions ).

  • avatar
    MKizzy

    It doesn’t help that some drivers are relying more on their safety nannies instead of their own common sense to keep them out of trouble while others don’t adjust their driving for rain because they think AWD gives them unlimited traction.

    • 0 avatar
      Lorenzo

      They’re not just relying on the safety nannies, they think they’re magic. If you’re old enough to remember when ABS first became available, then you remember people who honestly thought it would stop their vehicle on a proverbial dime.

      • 0 avatar
        tankinbeans

        I work with a lady who relies 100% on her backup camera when reversing into a spot. Also does the whole thing where she pulls nose first into 1 spot to reverse into the spot across the way that she’s aiming for.

    • 0 avatar
      Ubermensch

      Not to mention how many cars I see with tires worn down to the wear bars or worse. Wet traction drops dramatically when a tire get down to 4/32″ of tread and should be replaced at that point or earlier.

  • avatar
    gearhead77

    Everyone drives too fast and too close when its dry, so they can’t make the adjustment when the rain falls. Add into this the obsession with mobile devices behind the wheel and it only gets worse.

    Most of the driving public pays no attention to their vehicles until something is wrong, especially the tires. Just look at the tires on most cars as you stroll through a parking lot or along a street. More than a few are barely tires, let alone have any tread depth for removing water. It’s not just old cars or cheap cars either, it’s new(er) and expensive stuff too. I’ve seen Mercedes with the steel belts showing through. And as some others have mentioned, when it is time for replacement, its the Linglong SingSong Happy Best Economy tire or the cheapest thing out there.

    I know that state inspections are not popular among many here and that “mechanical failure” doesn’t account for much in terms of the accident rate.

    But the best way to avoid an accident, besides an attentive driver, is having tires with tread and brake pads that exist, along with a minimally functioning steering and suspension system. When I used to commute to Cleveland from Pittsburgh, I’d see a lot of Ohio tagged cars on the side of the road, especially after the rain. I now drive to DC, through MD and VA, both of whom have state inspection. It’s not that I don’t see derelict cars, but less of them.

    As enthusiasts, we are in tune with our vehicles and the road. Your average driver is not, driving is a chore and the car an appliance to do it with. Most people only service their appliances when they break, they view their cars the same way.

  • avatar
    -Nate

    Ha ! I read the part about old oily California highways, nothing has changed because it rains so infrequently here the oily buildup is the same, along with nails, sheet metal screws and God alone knows what all else yet I still see Motocylists driving the center every single day, fools who have no training much less common sense .

    The other thing about Southern California that I don’t understand is this :

    When the rain comes, most drivers _Speed_up_ ~ presumably to get out of the rain faster but they of course also brake too hard and go sliding into something/ someone……

    I’m that damnfool who’s passing you on the left at post legal speeds when it’s clear & dry and plodding along at whatever speed I deem prudent in the far right lane anytime there’s rain .

    Always on good tires, not just tread, actual good tires, properly inflated by chalk testing .

    When I built & sold affordable used cars, I made sure every one had good brakes and tires with treads, no baldies allowed, I’d try hard to find matched pairs for use as axle sets, I din’t care about the brands and so called them “my favorite brand ‘rondunblack’ ” =8-) .

    -Nate


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