Many speed limits are arbitrarily low. People are rational (excluding outliers) and drive the speed they feel safe driving, signs be damned. On primary roads th

Many speed limits are arbitrarily low. People are rational (excluding outliers) and drive the speed they feel safe driving, signs be damned. On primary roads the way limits should be set is by monitoring traffic speed and making that the limit. Instead, you get the "think of the children" irrational folks forcing lower speed limits on everyone. You highlight one exception. In areas with high population density and wide, high quality roads (much of the USA) you may need lower speed limits than what people feel they can rationally drive. Instead of just posting limits you need to add traffic controls that force lower speeds (eg stop signs, speed bumps).