From the Cop side: Many years ago when I was a rookie cop first learning how to do police work, I was assigned to work with a traffic officer. I’ll call him “Jim.” I had the privilege of spending a whole 2 weeks with Jim and learned a lot about crash investigations. (There are very few “accidents” but lots of car crashes.) Most citizens call them accidents, but when a trained investigator looks at the mess, he or she can usually figure out in a short time which driver or drivers were at fault. The usual reasons for the “crash” are because one or more drivers violated some traffic law, or law of physics.
When you take away that "one factor" that if it had not happened, you wouldn't have had a crash---that is then your Primary Collision Factor PCF.
One method I was taught at got pretty good at was estimating the speed a vehicle had been traveling at just prior to the crash. There were a few ways to figure this out, but one good bit of evidence often found was the skid marks left on the pavement.
Friction and"The Stopping Force"
A skidding vehicle is decelerated at a rate which is related to the frictional force generated between the skidding tires and the roadway. The friction is dependant on the weight of the "coefficient of friction".
(This may look like Bosnian writing, but it’s not) µ = V2 / 255 S
The following steps are used to find the coefficient of friction:
Now keep in mind, in my early days of police work, we didn’t have the really good pocket calculators that are around now. Some of this we had to do on paper.
Then I found a book with a chart that had all kinds of skid factors, so you could just look on the chart and be close enough.
I got pretty dang good at this shit…then something happened…in the 1990’s they came out with anti lock brakes. So much for all that skill and training…now the dang car would try to actually help a driver stop without skidding. Crap, no more skid marks.
But what do you do when the car you are looking at during an investigation violated the laws of gravity? Many of these flying cars are still unforgettable over 20 years later.
1980: I was on patrol in the nice friendly city where I started out working. I was dispatched to a motor vehicle accident with possible injuries. I responded from a few miles away with my emergency lights and siren on (Code -3). Upon arrival, I found a 1970’s something GM product on its roof with several yards (meters) of debris scattered along the road. The speed limit on that road was 35 MPH, so at first I had a difficult time comprehending how a car could end up like that.
I parked my marked patrol unit in a manner to protect the crashed vehicle and myself while I checked for injured persons. When I got up to the crash, all I could see were a pair of female legs sticking out the passenger side window. That was the only part of her body I could check for a pulse---but I lacked the Human Anatomy background at that time to know where to find a pulse besides the carotid and radial pulse (neck and wrist).
So, I did the next best thing and yelled: “Hey lady, are you OK?”
She moaned and moved, so I figured she was still alive. Then she started to swear…and that was when I could smell the “strong odor of an alcoholic beverage upon her breath and person.” She was alive.
No need for me to say that she was a very intoxicated driver. She went to the hospital and was booked in abstention due to her injuries. She fully recovered from the crash by the next day.
But, what a mess. I had to do the “T.C” (Traffic Collision) report. I blocked off a lane of traffic and got out my “roll-a-meter” and walked from where the car had landed, back to where it had first impacted the curb, brush, fire hydrant, street signs etc. It left only 50 feet of locked 4 wheel skid marks before it impacted the curb.
Then it lost control, went sideways, and landed on its roof….and slid for about 100 yards.
I had no way to figure the speed of a metal roof slide….maybe at least 85 MPH?
More flying car stories to come.