In Illinois, the minimum highway speed is 45 mph. Driving in the right lane, I get a lot of dirty looks at 45 mph, but it's perfectly legal. As a cop, I will tell you that, yes, we do look at slow drivers as potential drunk drivers, but there's a lot more factors than that. Probable cause can't be established by simply observing a vehicle operating below the speed limit (as long as it is at or over the minimum posted speed).
Most cops know about hypermiling (I know I get all sorts of crap for it from my co-workers). Just do what I do: Stick a "Hypermiler" sticker on your back window. That's enough to let us know that you're probably not a drunk
