lane drifting

On a multi-lane road (usually a highway or mainstreet), lane drifting is when a car suddenly begins 'drifting' over the lanes, usually because the driver isn't paying attention, or cannot see the lanes because they aren't painted well enough.

Usually they'll hover between two lanes, going the speed limit, and holding up traffic in both lanes.

I was stuck going 65 because the guy infront of me was lane drifting between the left lane and center lane, and was apparently oblivious to the chorus of car horns being layed upon him.