When your traffic lane is mostly a straight line in 3D and measured in 1000's of feet rather than just a few feet autopilot mostly just needs to maintain headin

When your traffic lane is mostly a straight line in 3D and measured in 1000's of feet rather than just a few feet autopilot mostly just needs to maintain heading and speed. You can get autopilots for boats as well and they can even do collision avoidance using radar, but its non obstructed 2D space with no real lanes in open water and lanes measured in 100's of feet in or more in channels. Cars share such close proximity with obstructed curved paths that makes a safe "autopilot" orders of magnitude more complex which should be obvious. There is just no comparison due to the space constraints cars must navigate actively.