That is not the steady state. When a car gets in front of you and eliminates your three second gap, it does so so it can continue at the speed of the traffic ah

That is not the steady state. When a car gets in front of you and eliminates your three second gap, it does so so it can continue at the speed of the traffic ahead. For you to be limited to 20 mph, the other cars would have to get in front and slow down. I feel that in practice I never have to do more than take your foot off the gas once in a while.