Sure, but in my experience people who are speeding at 10-20 mph on 35-mph-limited mixed-user surface streets are doing both. That's true as well on rural highwa

Sure, but in my experience people who are speeding at 10-20 mph on 35-mph-limited mixed-user surface streets are doing both. That's true as well on rural highways with hidden curves and possibly animals or tractors, or complex urban interstates with lots of traffic merging. These account for a majority of the driving people do. The case of a rural interstate with few interchanges is what people mostly think of with speed limits, but many of these have already been raised to a limit of 70–80 mph. People are bad at assessing risk and bad at awareness of road conditions. And I think learning to disregard posted speed limits corrodes regard for other rules of the road, like stopping at traffic lights.