It’s both because there is more than one kind of road.

America really likes stroads which give the impression that you can safely travel at speeds that are actually dangerous. We do that often in neighborhoods where we should be going 20-25 max but the design of the roads encourages us to drive faster. Since the speed limit is often actually at a safe speed, the issue of speeding is about the design of the road and not the speed limit.

Larger roads like highways, freeways, and expressways are designed for high-speed travel but often have speed limits that are low for the sake of revenue generation. If you’ve ever driven through a small town where the highway design doesn’t change but the speed suddenly drops from 65 to 35 you know what I mean. In those cases the problem is with the arbitrarily low speed limit as some states have raised the cap up to 80 and have not seen a substantial increase in accident-related injuries and deaths.

Connector roads often suffer from one or the other problem listed above. They are either designed to make you feel like you can go 60 when you should be going 40 or are set at 30 when you could safely go 40. The road design needs to match the safe speed by making drivers feel unsafe when they exceed that speed and not unnecessarily penalize them by not putting the limit lower than that speed.

Both of those result in speeding but have different causes.