

There was this study (not car related) on how well fines work, turns out if they are an absolute value (like in most cases) that is relatively low to ones wealth, a lot of people stop caring. Also, people are much more likely to break the law if they believe there is a high chance of getting away with it. So just having a sign might fix nothing, if the people to do not fear the penalty enough
Keep sharing them, cause I like the trapdoor solution a lot more than a complex road sign ;)