In the southwest, we have what's referred to as one-light towns. Maybe this translates to other parts of the world as well, but essentially a town so small that they only need one stop light to regulate traffic. These are the definition of a sleepy town. As a specific example I'm well traveled is a stretch of state highway in Texas between Ft Worth and Amarillo called Hwy 287. As you get away from Ft Worth, and even west of Wichita Falls, the speeds are 75mph in places. This highway is dotted with these one-light towns. Just before each town, the speed limit slows to 35mph. It's easy to say it's just for revenue purposes, but as a sibling comment points out, the noise is the primary issue. Sure, safety for those that might dare to cross the street as a pedestrian is just a side benefit. However, the opportunity to pad the county coffers near these speed limit changes is too great to not be heavily speed trapped