I disagree. There are two roads near me with a limit of 55 mph, and traffic on those roads regularly moves at 75-80. Driving 55 becomes dangerous when all of the other traffic is going so much faster, because nobody expects you to be that slow. You risk getting rear-ended, and if traffic is heavy, people who end up behind you now have to merge into a much faster lane of traffic to get around you.
Yep! That was the first qntm book I read.