I thought this was pretty interesting:
http://www.roadandtrack.com/features/web-originals/features-web-originals-anatomy-of-a-high-speed-car-crash?src=rss&src=spr_TWITTER&spr_id=1459_12900271
Basically says that a 40mph offset front end collision with an immovable object is fatal. If your vehicle is more than 20 years old, that number drops to 20mph.
It's a pretty strong endorsement for wearing a helmet at all times, too.
