Waymo's L4 is limited to a few geographic areas where it has mapped (and continuously re-maps to catch changes) every street, light, stop sign, traffic sign, etc., down to the millimeter. As I understand it, their LIDAR looks at the surroundings (pre-mapped, remember) and determines the exact location of the car. They use this to essentially drive like they're on rails. They don't need to read lane markers because they're always in the right place based on the maps. But even Waymo recently said they will still need safety drivers for at least a few more years. So that doesn't sound like a true L4 to me. If this isn't correct, I would appreciate it if someone would educate me.
This is not completely accurate. Yes, Waymo maps an area and uses lidar for precise localization. HD maps provide useful information to help increase safety:
"Before our cars drive in any location, our team builds our own detailed three-dimensional maps that highlight information such as road profiles, curbs and sidewalks, lane markers, crosswalks, traffic lights, stop signs, and other road features. Rather than rely on GPS, Waymo’s vehicles cross-reference their pre-built maps with realtime sensor data to precisely determine their location on the road."
Safety Report – Waymo
But that is just one piece of how they do autonomous driving. Waymo cars do not just follow a preset path based on the HD map "like on rails". Waymo cars use all their sensors to perceive the world and objects and figure out the best path and avoid hazards. Waymo cars are able to change paths based on sensor data to avoid hazards or when there is road construction.
Here is a diagram from a Waymo presentation that shows how their system works. You can see that they use both the Map and the Sensors (cameras, lidar, radar) for localization and also feed the Map and the Sensors into their Perception to detect all objects etc...
The Waymo Support page also has some information on how Waymo does autonomous driving:
How Waymo experiences the world
A combination of cameras, radar, microphones and LiDAR are the eyes and ears of every Waymo car.
Waymo uses…
- LiDAR to detect everything around the car, like pedestrians, cyclists, or other drivers
- Radar to help detect objects around the car and estimate their speed, like other motorists traveling around it
- Exterior cameras to see visual information, like whether a traffic light is red or green
- Microphones to hear audio cues, like the sound of police or emergency sirens
To help it plan a safe path ahead while driving, the car can see up to 3 football fields away in all directions.
How Waymo drives itself
Waymo software is the brain of the car. Through the software, the car makes sense of everything coming from the sensors, and uses the information in real time to drive itself.
Waymo cars can...
- Navigate on city streets to get from point A to B safely
- Avoid hazards including by slowing down, changing lanes, or braking completely for a stopped car
- Adjust to unexpected changes in the roads like road work or closed lanes
- Obey traffic laws like stopping at stop signs, and yielding to pedestrians or cyclists
Learn how Waymo drives - Waymo Help
This is an excellent video that explains how Waymo cars drive:
As you can see, it is much more than just mapping, localizing and following a path. IMO, it is L4 autonomy because the car is fully perceiving the world and is reacting in real-time to do all the driving tasks and drive without human intervention, just in a given area.
I think a big reason why Waymo geofences is because they don't want a customer who uses their ride-hailing service to select a destination that would take the car in areas that they have not fully validated yet.
Waymo has removed the safety driver for some drives where they are confident that it is safe to do so. But they are not ready to completely remove the safety driver for all rides yet.