The "rumble bumps" were on a highway. Sometimes the highway was divided by a median strip, but other times the lanes of opposing traffic were only separated by a center lane that variously accommodated either direction of traffic. When that was the case, there were the strips of rumble bumps dividing the oppositely moving traffic in the center. A median strip of rumble bumps, so to speak.

I'd just never heard or read the term and wondered about it. There were also rumble bumps or strips on the far right to wake you up should you drive off the road--or just to let you know that you were venturing too far to the right. I, for one, really appreciated having those rumble bumps as an auditory and kinetic marker. I heard one person say that rumble bumpkins named rumble bumps.