Here in Massachusetts, the staties blow by you at 100MPH (and when people don't move over, sit on their tail and probably give them a good scare when they finally realize what's behind them). I generally see them coming from pretty far back (a car closing at ~25mph is pretty noticeable), move over, let them pass, then see how long I can follow. I figure that the cop
must be following the law and going a safe speed for the conditions of the road, so I can use them as a benchmark for what is considered acceptable instead of having to rely on the purely advisory signs.
Funnily enough, the slow cops and coplike vehicles that bunch up traffic are usually the ones with the least jurisdiction and least likely to give out tickets. Town cops going one exit on a state road, inmate transfer, game wardens, etc. This could of course all be fixed by having speed limits that reflected society, and GPS tracking of cops to make sure they're not immune from the law. But more likely self driving cars will make the whole situation moot - I'd gladly save fuel and make a 2hr trip in 3hrs if I didn't have to waste my attention on the vehicle.