I'm sorry, I meant 2-lane roads! Again, the chance of a car veering into another car on a less-than-busy road is very, very small. That then the cars would hit front-to-front would be yet another infinitesimal possibility added to the other, multiplying the difficulty. 
Obviously, these are very difficult things to determine, we're not able to ask the deceased their motivation. Even if we could, see my post above for findings about unconscious self-destructive behavior.
There are just far too many of these head-on crashes for me to believe they're all "accidental."