Main question: Why does a particular highway have roughly the same number of automobile-related deaths every year if a car crash is unexpected and dependent on the actions of individual drivers?
More detail: in Tennessee, they have those electronic signs on the interstate that occasionally show the number of roadway fatalities in the state for the current year and beneath that it will show the previous year. The numbers are almost always close, within a reasonable margin of error and accounting for both slightly more drivers on the road each year fur to population growth.
Having been in a serious car crash, I understand the seemingly arbitrary way a sequence of events can play out depending on multiple factors such as driver awareness, vehicular dependency, roadway conditions, weather, etc. Even a highly skilled and fully focused driver in a perfectly functional car on a road with no issues can be involved in a crash, say due to a different driver’s condition, a deer running out into the road, or a sudden gust of wind blowing a newspaper onto their windshield and obscuring their vision for a few seconds.
This may by a multi-part question, but it’s been in the back of my mind for years now and I woke up today wondering about radioactive decay so I started reading about isotope decay. That’s not really what this question is about though, but the seemingly random probability of an isotope decaying in an independent manner (not related to the actions of any other isotopes nearby) made me kind of connect these two ideas and start to wonder about it again.
So getting back to the roadway fatalities, in this case for the state of Tennessee, I found the 20 year statistical data at the site linked below. It shows some ups and downs over the years, presumably with the reductions coming from improved safety features in cars, yet the total number for 2020 (1,221) is closer to the total for 2001 (1,251) than it is to the total for even the previous year 2019 (1,148).
So despite population growth and enhanced safety features, we are kind of right back where we started, or rather, where we’ve always been.
I could also expand this question to cover other events that should ideally never occur, such as murder. Why does something as abominable and world-shattering like murder, at least from an individual perspective, happen with roughly the same frequency and rate when looking at a large sample size? Shouldn’t something like that be the exception and not the norm? Is it somehow related to density?
This has me wondering about probability, fate, design, and all sorts of things both rational and irrational.
Anyway, thanks for reading this. Even if nobody responds, I think it’s helped to just get it out in writing for the next time I think about this in a few months.
TLDR: Why do independent actions and events that deviate from the norm happen with almost certain predictability?
In: Mathematics
So this is a statistical principle. When you have an event with a certain probability, like a car accident, there will be some variation day-to-day or week-to-week. But the larger the data set you have, the more likely the numbers are to inch closer to the true statistical average.
So let’s say 1 in 1,000 cars that pass by crash in this highway. (That would be really high but for our purposes we will use a clean number.) if you start counting at a random time, and the first 1,000 cars pass, you should see about 1 accident but you may see zero accidents or you may see 2 or 3. The sample is small enough that you’ll have some random variation. If you watch 5,000 cars pass, you’re still likely to not see exactly 5 cars. But if you watch a million cars go by, it’s highly unlikely that the data you gather will deviate from the true statistical likelihood of a crash.
The data you’re citing will be on a highway that millions of cars cross a year so the states will be fairly stable, accounting of course for changes to the population, the road itself, the types of cars on it, and whatever disruptions COVID caused to people’s driving patterns.
Overall driving a car is much safer than it used to be. The tots number of vehicle fatalities are less than they were in the 70’s and 80’s despite there being twice as many cars on the road and a lot more miles driven on average.
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