I can't imagine there's that many opportunities to drive particularly fast on the M1, isn't it basically a traffic jam day and night? Maybe at 3AM...
The US highways speed limits don't seem to conform to 55 MPH much these days. Maybe beltways or particularly busy highways but in the last few years of
driving in various States I've seen everything from 55 to 75 MPH on many varying highways. I think the Denver to Wyoming road we drove on was 75 MPH.
Around Baltimore where I'm from, there's a wide variety of 55, 60 and 65 MPH highways depending on average amount of traffic and distance from urban areas.