The term "black ice" is a very interesting (and dangerous)
phenomenon. It describes a situation where a road surface becomes
coated with a very thin layer of perfectly clear ice. The (usual)
black color of the road surface shows through the transparent thin
ice layer, but the surface is as slick as a skating rink, hence
There are several very similar weather circumstances that can result in black ice. Here is a common one. The weather appears rather clear and the temperature is relatively mild, with an air temperature slightly above freezing, say 35°F. The ground (and road) is at a temperature below freezing, due to an earlier very cold night or due to rapid radiative cooling of dark-colored (black) surfaces. In any case, the road surface is at, say 28°F.
Now, a VERY light rain, actually just a mist, begins to fall. So little rain falls, and the mist droplets are so small, that no rain even hits the windshield of a vehicle, so there is no clue that there even IS any rain falling. Because the droplets are so very small and the air temperature is above freezing, none of this precipitation is snow or sleet, and it is all normal raindrops.
Once these tiny raindrops (which are only slightly warmer than freezing) hit the colder pavement of the highway, they immediately freeze. After only a minute or two of this phenomenon occurring, the entire surface of the highway can become coated with this invisible coating of ice. There is no indication whatever to a driver that the road is anything than a normal, safe, dry highway. But, in reality, it is as slick as a skating rink.
I have done a LOT of driving in my life. I have encountered black ice on about a dozen occasions so far. Many of those experiences were when I happened to be traveling at fairly slow speed, and the vehicle just slowly slid safely sideways off the road. There have been exceptions!
I later concluded that when I had stepped on the brake, I must have locked up the wheels, or at least some of them, which stopped spinning. The result was that my car ALSO started sliding toward the center of the road, exactly the opposite of what I was trying to do!
So, here we were, two cars hurtling toward each other at a total speed of around 150 mph, absolutely head-on, because we were each centered on the center lane marker. It was the weirdest feeling! I felt totally helpless as to doing anything to avoid a really bad collision. However, I also didn't really feel that I was in any serious danger myself, because I knew how massive my car was and how tiny the VW was. I was bracing myself for this head-on impact. I even shifted my body to being very near the door because when I had been really little, an older relative had been in a head-on collision and I remember seeing the wrecked car where the engine was right next to the driver because it had gotten pushed so far back due to the collision. I didn't really think that little VW could push a Cadillac engine back like that, but I was being able to be very logical and not really afraid. I have to believe that the VW driver had to have a yellow and brown stain on his seat!
Our two cars were around 100 feet apart, and still hurtling toward an exact head-on collision. Since that meant that the collision was now only 0.5 seconds away, and unavoidable, I remember closing my eyes (I don't know why!).
As it happens, my wheels were still aimed to the side, even though they were sliding exactly straight. I suspect the same was true of the VW. In any event, apparently there must have been a little dry spot on the road. While my eyes were closed, I felt a sudden sideways push (like when a roller coaster goes around a corner). After about a second of having my eyes closed, I realized the collision should have already happened! When I opened them, my car was angled toward the shoulder and I had to do some quick actions to keep the car from going out into a field. When I felt I was is some control, I looked in the rearview mirror and saw the VW also on the other apron.
I have no idea why that accident didn't occur! I was tempted to think that God was somehow involved, but I am not sure about that. All I know for sure is that I learned what black ice is!
Possibly a mile ahead, I saw lots of red flashing lights. My friend was asleep in the passenger seat. Because of the all the flashing lights so far ahead, I very lightly stepped on the brake. Not so much because it was necessary yet, but because red flashing lights probably represented Police, and I was driving way above the speed limit!
When I stepped on the brakes, I was rather amazed to notice that there was absolutely no effect whatever! I stepped on them again, harder, with again no effect, but now I happened to look at the speedometer. It was registering zero mph! And I knew we were moving at around 90 mph! This was a problem!
From the previous experience, I quickly realized that this was a black ice situation. I tried turning the wheel back and forth, but there was no effect. I tried accelerating and the brake pedal, but no effect. We continued to slide down the highway at around 90 mph. Fortunately, there was no other vehicle in sight, so, whatever was going to happen would not be complicated by other sliding vehicles. That was good! But, very gradually, the body of the car rotated. I suppose that there was slightly different friction at some parts of the road than at others. In any case, the car is now sliding exactly sideways down the highway, still at nearly 90 mph. NOW I was scared! If we would have hit a dry patch of highway then, the tires would have gripped, and the car would have instantly rolled over a bunch of times, and there would be great doubt about our survival. That was one of the scariest moments I have ever had while driving!
I'm pretty analytical, and I figured that it would be a good thing for me to apply the "parking brake". That brake ONLY locks up the rear wheels. Then I made sure not to do anything that might keep the front wheels from starting to roll. (The car is still sideways.) I turned the wheels as far as I could toward the front. I think they must have started to slightly roll.
Sometimes, it's handy to be a Physics major! I knew that there was a bunch of equations about static coefficients of friction and dynamic coefficients of friction. I didn't have time to do any of the calculations, but I quickly developed a plan based on the concepts!
In any case, the car very gradually started to rotate back to where the headlights were again in front. By then, we were probably down to around 60 mph, and I was starting to feel a little safer. I left the parking brake on and made sure to not touch the brake pedal. This combined the slight slowing effect of the locked up rear wheels with a slight steering effect of the rotating front wheels. Eventually, we got down to about 20 mph, which is the speed we eventually passed a horrible accident that was the reason for all those flashing lights. Eventually, my adrenaline level dropped to fairly normal levels!
Like with the previous incident, I sometimes think back on what might have occurred. If we had been there a while earlier, we may have been part of that original horrible wreck. If we had been there even a few minutes earlier, there would have been no red flashing lights to inspire me to consider slowing down, and we might have arrived at the accident site, sideways, at 90 mph. If there had been ANY other vehicles near us when I was dealing with our problem, well . . . If we had encountered some dry pavement while we were sliding sideways at so high a speed, well . . .
Again, I have no logical explanation for why we didn't wind up in a terrible accident that night.
In March, 1999, I was driving home after a day of work, in the afternoon rush hour, going west along I-94 near Hammond, Indiana. Since it was the rush hour, the road was filled with many vehicles. The traffic was all traveling at around 45 mph, as there was substantial snow on the highway. My Corvette was in the leftmost of the three lanes of traffic. It was late enough in the day where everyone had their headlights turned on.
In other words, this was a pretty normal rush hour for that time of year. There was no vehicle right next to me, but I had earlier noticed that two semis were just a little ways back in the other two lanes. About six car lengths (100 feet) ahead, there were three cars about even with each other, with the middle one slightly ahead of the other two.
I suddenly saw that the headlights of that middle car flashed at me! It had somehow started rapidly spinning, apparently due to unseen black ice. As his car continued to rotate, it was not right even with the two other cars next to it, and the front and back of his car hit both of them. This was beginning to look like one of those big crashes they sometimes have at the very start of a NASCAR race.
The car directly ahead of me was light-blue. It was now cross ways in front of me, and there was obviously no possible way to get past it, even if there weren't even worse things happening in the other two lanes. When I touched the brake, there was little effect, so I realized there was black ice on the highway. It seemed certain that I was going to T-bone into the side of his car. Since the driver's side was nearest me, he seemed to be is tremendous danger of me crushing in the side of his car. With this in mind, I attempted to aim my car toward the median apron. The front of his car still blocked that too, but I thought he would be slightly safer if I wound up hitting that part of his car.
Of course, by now, all of the dozens of vehicles were sliding down the highway. The real danger was probably those two extremely massive semis that were behind. I actually also chose the median apron because I thought that would be the least likely place those semis were going to go through, I suppose a somewhat selfish self-preservation motive!
So, now, I have managed to get my car entirely on the apron, and I am REALLY close to the vertical concrete divider structure, and everything is still sliding down the highway. Remember the original spinning car? It still continued to spin, and, now that the light blue car was sideways, it hit it again, causing the blue car to again rotate. From my point of view, the timing was astounding. The blue car rotated like one of those rotating gates at a subway, very briefly straightening that car out enough for my car to pass on by it on the apron. And, moments later, it was again crossways! Somehow, my pretty Corvette never got hit at all!
A few days later, when I again passed that same area, I looked carefully at the median concrete. During the excitement, I had actually TRIED to slide the side of my car against the concrete to slow it down, so I wouldn't hit that guy so hard. Since the accident seemed absolutely unavoidable, I intentionally tried to do some initial damage to the side of my car to minimize how badly the blue car driver might be injured. But when I had gotten home, there was no damage to the side of the car, and I was really confused! It turns out that some highway designer had sloped the sidewall shape of that concrete median! The sidewalls of my tires were severely scuffed, and the rubber was still on the concrete median walls! Thank you, whoever you are!
I suppose you have noticed that here was yet another black ice incident where I should have been seriously injured (or worse) and yet there was no damage whatever to my vehicle or myself. Again, I have no logical explanation.
I was driving home from work (during college I worked for Sears) at around 10 pm one night. It was probably March, but the temperature seemed rather warm, so I lowered the roof when I left work. So, I'm driving along at around 45, in Chicago Heights, Illinois, and up ahead, there's a 45 degree right turn I need to make. Most people slow down for turns, but I always strengthened the anti-sway bars in my cars and did other things to them (I was a motor-head and enjoyed making modifications to cars), so I could go around most curves and turns far faster (but safely) than other cars could.
On this particular night, there were two additional variables that I had not known about. The first was that there was a fairly small patch of black ice right near that turn. The other was that, when you move several hundred pounds of roof structure back four feet to put it into a trunk, the car handles WAY differently.
Again, fortunately, there were no other vehicles in the immediate area, although there were several close enough to see what happened. As I shot up to this corner, the front wheels actually started to go around the corner. But that big old weight at the very back end of my car quickly broke the back wheels loose. The car started spinning like a pinwheel, again sort of like you sometimes see in NASCAR races!
At this time of year, the farmer had not yet planted anything in the field that I pinwheeled into, so that was good. And fortunately, the power company had put its utility pole about 10 feet away from where I passed through.
Now, because of the fairly slow speed involved, I don't think I was in any mortal danger, but I thought this might be another illustrative example of black ice. And, the handling of a vehicle where its center of mass was seriously shifted rearward!
The weather was fairly mild, and I was already wearing my preferred summer shorts and flip-flop sandals. I DID have a light coat on because it was a little chilly. When I went INTO the store the ground was basically dry. But while I was in the store, a black ice situation developed. I had only needed a couple of small items in the store, so I wasn't carrying any grocery bags as I left.
It had become REALLY windy during those few minutes I was in the store, (this is near the windy city, Chicago!). My car was almost due east of the store entrance and the sometime 40 mph wind was directly out of the west. So when I recognized the black ice situation on the parking lot pavement, I got the brilliant idea of spreading my coat apart as a sail! I figured I might be able to slide out (on the very smooth bottomed well-worn flip-flops) as an option to walking! Sort of like those people-movers in some airports!
Well, it worked great! The smooth bottoms of the sandals were easily gliding across the parking lot, and I kept picking up more and more speed! I was SO pleased with myself! I was occupying myself in spreading my feet and trying various snow skiing and water skiing steering techniques.
By now, I am moving WAY faster than I could ever run, possibly 20 mph. Well before that, I had closed up my coat to reduce the sail effect, but I was not slowing down, because of the black ice slipperiness and the continuing very strong wind behind me. It was starting to dawn on me that I was going to have to start thinking about how to stop. I considered aiming directly at my car but an impact with a car at 20 mph seemed almost certain to injure me, and I could see the next day's headlines about an idiot that collided with a parked car and was in the hospital with assorted broken bones! I squatted down (to reduce my 'sail' area), I turned my body sideways, I tried everything I could think of.
Beyond my car, there was an eight-foot high pile of snow that had been cleared earlier from the lot. For a while, that was my preferred choice, because I figured that if I hit that pile, even at fairly high speed, I probably wouldn't be injured too badly. But I also noticed that across, in front of that snowpile, there was a path that lots of cars had passed through. I became pretty sure that the pavement there was probably not slick because of the motion and heat of the tires of those cars. So, I realized that I would probably never make it to that really safe looking snowpile.
I was already squatting down. I was sure that there were probably a lot of people watching my craziness (and my speed!), and I didn't see any obvious way that this was going to end in any classy way, so I just sat down! I'm sure it looked really stupid, but I just couldn't think of any better idea to avoid being injured at the time. It actually worked out fairly well. I only slid about 30 feet past my car. And I had a couple towels in the car to put on the seat so my wet butt wouldn't ruin the interior.
Another experiment with limited success!
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