but somebody either doesn't get it or doesn't care
That somebody is you. You're not following the conversation. Dashster was claiming that shipping companies had reduced the speed of their ships to adjust to higher oil prices. He was also asking if it would be possible to do something similar with tractor trailer trucks, once oil starts declining.
You responded by posting that the speed limit on a very few stretches of freeway in Texas and Maine, and freeways in the UK, had increased. Ghung, how exactly does that contradict the claims made here? That's obviously not even relevant to the claims made here.
Car traffic on freeways is something else because motorists also care about convenience and safety, not just minimizing fuel costs. Traffic fatalities are at all-time lows because of improved safety features, so maybe motorists would prefer to reduce their fuel consumption by buying more fuel-efficient cars rather than slowing down.
-Tom S