I used to teach driver safety and most folks were amazed when you give them a 30 metre (100 foot) tape measure and ask them to demonstrate thinking and braking distances from legal speeds (something taught in all driving schools but often not demonstrated practically). The most chilling instruction/demonstration was what damage could be done to the human body at relatively low (legal) speeds. Post accident clearing up is one of the most harrowing jobs there is. I'm glad that I no longer have to do it. I remember a local traffic officer who used to suggest that speeders should have a six inch nail araldited to the centre of their steering wheel and pointing towards them, when they got back behind it!