I have two fun stories about speed bumps.
My favorite is driving on a neighborhood street, see a sign stating a speed bump is ahead rated at say 20mph. Funny thing, I could have swore the speed limit sign I just passed said 25mph. Why is the speed bump a lower speed than the speed limit?
The other fun one is that your traditional speed bump is a major problem for fire trucks. Fire trucks have jack for suspension. Thus going over speed bumps is a bit of a hassle.
If they want to slow people down, there are two better ways. One is the rumble strips, those very small speed bumps that make the car shake slightly when going over them. They help remind you about your speed. The other is putting in a chicane (sp?) style turn in the road. I've seen many places where they do this to prevent a long straight section that would otherwise be a speeding zone.