This is an interesting wrinkle into an old truism about the dangers of backpacking vs. driving. I don't know anyone who has died backpacking or driving to the trailhead. I've read stories of people who have died backpacking and stories of people who have died in car accidents on roads near trailheads, however the car accident stories usually involved people driving dangerously on the twists and turns of mountain roads for fun. i.e. they were there for the recreation of driving dangerously not for the recreation of backpacking.

To muddy the water further, you could take into affect the impact on life expectancy of exercising. If I'm backpacking, I'm exercising and not sitting in a chair doing work or watching TV. That will have a positive impact on my life expectancy. I work in an office and I tell people the most dangerous thing we do is sit in a chair and stair at a computer screen all day.