I think training is the key, but not just vehicle training. Have training sessions over say 4 weeks, that show all the photos and footage taken from fatal crashes. Repeatedly. Show them a baby that has been flung from a car, show them a mother who's head is 50 meters from her body, show it all. Show the vehicles. Show the charred remains. It may or may not work, but at least it is giving them more of a chance to see consequences and maybe just flash a bad image in their head the next time they want to give it a squirt.