Complex sentence: The best thing to do is drive down the road embankment if that's not possible and a collison can't be avoided, hit the rear part of the elk so the horn don't smash through the windscreen.
Split into simpler sentences: The best thing to do is drive down the road embankment. If that's not possible and a collison can't be avoided, hit the rear part of the elk so the horn doesn't smash through the windscreen.