perception, planning
Paint is a suggestion. The actual question is where the vehicle is allowed to put its tires.
A hiking trail can disappear under leaves and you still know where the hill lets you walk. Lane paint is the trail blaze. Drivable space is the hill.
Lane lines help because they are a shared convention. They also vanish, contradict each other, or lie. Construction paint fights old paint. Snow covers both. A double-parked car sits on a perfect line. An emergency vehicle occupies the only legal lane.
Lane paint is the trail blaze.
A stack that only follows paint is brittle. A stack that only hugs “free space” can drift into a bike lane or an oncoming shoulder that happens to be empty. Mature systems keep both ideas: a map of markings, and a map of where a vehicle of this width can physically go without hitting curb, cone, or bodywork.
Those two maps disagree often. That disagreement is a planning problem, not a camera problem. Do you stay in the faded legal lane and clip a cone, or do you use the empty oncoming sliver that every human is already using? There is no universal rule. The long tail of urban driving is mostly these small negotiations between paint and space.