Another data point - Deaths on Texas Roads are 1 in 70 million. while not all highway driving, I would assume that the distribution is pretty skewed in favor of it. But maybe more pertinent More than half of the deaths occur at speeds > 55mph. (assuming this is highway) -- http://www.iihs.org/iihs/topic... This seems to suggest that your likelihood of dying is the same on or off the highway, though I imagine you are probably more likely to get into an accident off the highway, just not likely to die from it. Unfortunately, you would need to get a number on the the miles driven on and off highways, I couldn't find it quickly.