Keeping the car in its lane amounts to keeping it from hitting anything. In any case - lane markers or not - controlling the car on shared roadways requires loc

Keeping the car in its lane amounts to keeping it from hitting anything. In any case - lane markers or not - controlling the car on shared roadways requires localizing it in terms of its environment. A high-fidelity map of the environment improves the localization accuracy that can be achieved from noisy sensors. If the map is more accurate, you can tolerate more noise from the sensors.