This is a simple story with a powerful message.
A few years ago there was a head-on crash on the Golden gate Bridge. This was the third in a decade. The Golden Gate Bridge is run by local Bay Area politicians, so they proceeded to look for a solution to a perceived problem.
In the meantime, this six lane bridge, which usually has 3 lanes going each way goes to 2 and 4 at rush hours. Most of the day the speed limit is 45 miles an hour. It works. Most drivers accepted the 45 mph limit because they can see that lanes three and four are going the opposite directions with only a few inches separating the cars. Clearly dangerous.
The other Bay Bridge that goes to Oakland from San Francisco put up a 45 mile an hour speed limit in imitation of the Golden Gate Bridge. The new speed limit on that bridge had no impact and didn't change the driving speed, which averages 60 miles an hour in moderately dense traffic. People saw no danger on the Oakland Bay Bridge because it is one-way traffic. They ignored the new posted speed limit.
I pointed this out right away when I saw what was happening; people do not obey laws that do not make sense to them. Conversely, people accept laws that make sense. If they know about them. (We don't know about nine out of ten laws the are intended to govern us.)
We had a wonderful test of my thesis recently. The directors of the Golden Gate Bridge decided to put in a multimillion dollar movable barrier to divide traffic on the Golden Gate. Once it was installed, people could see that cars would not cross from the opposing lanes of traffic through the barrier. So they increased their driving speed to a reasonable level. Here's the local story.
Lesson: people obey laws that make sense to them.
P.S. ( Also see Phil Ossiferz Stone's comment below. People will defy serious laws that don't make sense.)