Edited the last sentences in my post for clarity Most recumbents will certainly not be very functional for mountain biking, even though it has been done. Horses for courses! For trails and uneven surfaces like gravel, hardpacked snow, etc, uprights work better as a general rule. I do think though that recumbents generally are safer, as the head doesn't go first in the case of a fall or a crash, but I certainly see why they may be perceived as less safe. I like all kinds of bikes though. I have been using traditional road bikes for many years, and I will probably keep riding both recumbents and uprights.
I'd be far more worried about the mass of the car vs my bike/body, especially if I'm below the line of sight of the drivers (I know you can fly the flags and all that, but I've not been seen on a large upright motorcycle with a headlight on by someone making a left hand turn in front of me, too ). I've been saved by my helmet a few times, cars or no, tho I never really thought much about the head being a few feet higher and farther forward than on a recumbent.....
IMO that's one of the best parts of mountain biking....no cars to contend with (well, most of the time, we do have some traffic on our dirt/gravel roads to access trails). Have always wanted to try one of the aero type recumbents with a full fairing just for the speed aspect....but would prefer a closed course for that OTOH.