American here, in practice no. They are generally only the upper bound for dense neighborhood streets, throughout most other roadways you will be considered a poor driver if you go lower than the speed limit.
replyConsidered a poor driver, and you can be ticketed for impeding traffic. I'd guess you are also more likely to undergo a field sobriety test if and when that time comes.
replyWhere I live the major strode has a 45 mph speed limit and during most times of the day we only get to 35 mph but people make up for it by running the red light
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