^Centre line rumble strips work great. We've had them for quite awhile in Nova Scotia. We've even taken it a step further and installed double rumble strips on some sections of Super-2.
Google Streetview of Highway 101 west of Coldbrook.
The fun rumble strips are the ones that run across Highway 104 at the Cobequid Toll Plaza. Those things will wake up your passengers. No warning and no way to avoid them. They used to wake me up and tell me we were only ten minutes away from grandma's house. Now that I'm always the one driving they aren't as pleasant.