Half Dome Hike Risk vs Driving to Yosemite Risks

National Parks, yosemite, yosemite half dome california

I have just  survived a top ten dangerous hike in the most dangerous National Park so naturally I’ve been wondering just how dangerous that hike was.  Typically we overestimate “dramatic” dangers like lightning strikes and hikes and underestimate the mundane, greater dangers of driving cars and riding our bikes around.

However in the case of Half Dome it appears there is a bit of death risk, albeit still pretty small in the scheme of things.

http://www.backpacker.com/october_08_americas_10_most_dangerous_hikes/destinations/12631

Our odds of survival were always good, but Yosemite has been a dangerous park, especially last year 2011 when  18 people (!)   died there :  http://www.nytimes.com/2011/09/06/us/06yosemite.html?pagewanted=all
Spooky description of a 2007 fall off the cables:
Book about Yosemite deaths.
Base jump off the place where we took pix:  http://www.youtube.com/watch?v=WdxU2tDbL54
Of course you have to compare the small number of deaths on that hike over many, many years (20 on dome, 60 on trail) with the huge number of people who *survived* their hikes, as I think we did (assuming no parallel universes where we didn’t survive), to get a reasonable risk calculation.   You also need to compare that risk to other risky things we do, such as *drive to Yosemite*.
I wanted to know which was more dangerous – the drive or the hike.   Obviously there are many confounding variables  (nobody was drunk driving, our hiking experience is higher than average, decisions vary with people, etc, etc, but here’s a shot at the answer  …..
Let’s assume that the  20 dome deaths are since cables were installed by The Sierra Club in 1919  (hey, THANKS Sierra Club!):
Now we need to estimate the number of people who have made it up there as we did.   Ranger guy below the dome and internet tells us it is now about “350-400 per day”.   That would be current high season with permit restrictions so hard to know the past until I can find more records.  But we know that the low season (winter) is about 0 per day.   Probably far fewer people in 1919 than now, so let’s *wildly guestimate* that on average, since 1919,  100 people per day go up, and that almost all that traffic is during the high season of June, July, August, September when cables are elevated with the metal rods  (in the past and in winter they lay flat on the surface).  100×120 days = 12,000 people up per year.  90 years of cables x 12,000 =  1.08 million ascents of half dome over 90 years.    ROUND THIS WILD GUESTIMATE to one million people up  half dome over all of human history.
We now have 1,000,000 people who went up and 999,980 people who come safely back down.  20 of the million, sadly, died on half dome.   Thankfully, every single one of us remains in the 999,980 group of happy Half Dome hikers.
Your chance of dying on the final half dome portion of the hike is, very very approximately, if our assumptions are reasonably accurate, about 20 / 1,000,000 or one in  50,000.    We could also state this in this fashion if our assumptions are correct:
“For every 50,000 people who go up the final portion of the half dome hike … one will probably die”.
For extra drama we might note that we had 6 people on the hike so the (pre-hike) odds that one of us would die were 6/50,000 or 1 / 8333.
 
Now we need to compare this to our 900 mile car trip home.   Car travel is one of the more dangerous things we do on a regular basis.   VERY ROUGHLY in California there are 1.21 deaths per 100 million miles travelled
We did not travel 100 million miles so we need this calculation to figure out deaths per Yosemite trip:
The chances of dying during 900 miles of car travel in California:  900 x  [1.21 / 100,000,000] =   .00001 deaths per Yosemite trip.
So, on average of all drivers and cars and circumstances, the chances that somebody will die on a trip of 900 miles in California are about one in 100,000.      Put another way this means that, very approximately:
” For every 100,000 people who take a 900 mile trip to Yosemite by car, one will die ”  
 
So if all these assumptions are pretty reasonable, than we can state that the half dome portion of the hike with its one in 50,000 chance of death, is about twice as dangerous as the car ride with its 1 in 100,000 chance of death.  

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