That question is the easiest one. The perception of getting caught changes people's driving behaviour.
Engineering will always give you your greatest returns. Our vehicles today, driven at around 70 or 80 kilometres an hour, can crash, and everyone will pretty well survive in them. Engineering, then, is the first. The threat of enforcement is the next one. Education is the least effective.
Although what you just said sounds like a lot of money, it's not much money in terms of advertising to change a campaign against people who are going to be using probably 60 times that amount of money to get their message across.
If you want to reduce injuries, look for engineering first. The threat of or perception of enforcement is next. The last one is education.