Some people have brought up very good points regarding minimum speeds, and I think there is a lot of merit to the idea that, often, it is up to the law enforcement officer's discretion. Just thinking about California specifically:
In rural, farming areas, any slow moving farm vehicles have to display a placard if they are driving on posted roads (typically, with a maximum speed of 15-25 mph). Depending on interpretation, a pickup truck could be considered a farm vehicle, and it definitely is if it is towing equipment (placard is required).
NEVs are not allowed on public roads with posted speeds greater than 35 mph because, as we know, they are not capable of achieving posted speeds much greater than that. Again, a law enforcement officer could interpret that to mean that vehicles must be driving close to the posted speed limit.
Also, the fact that California highways attempt to segregate slower moving traffic (e.g., instructing slow movers to stay in the rightmost lanes) can be interpreted as a admission that a large discrepancy in speed is dangerous. Again, an officer could consider driving considerably slower than the posted speed limit as reckless driving. Another example of this is in areas where the freeway's posted speeds are much slower than normal. For instance, southbound on the Grapevine, the lines between the lanes turn sold, meaning lane changes are no longer legal.
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