That's quite opposite to how autonomous systems should be built in the first place: start with isolated modules that do not depend on each other, and stack them

That's quite opposite to how autonomous systems should be built in the first place: start with isolated modules that do not depend on each other, and stack them on top of each other as the abstraction level goes up. If you have an automatic but a brutal, on-off style emergency-braking module based on, for example, lidar then it's much easier to develop another, maybe less aggressive but much smarter, auto-braking module based on the regular camera inputs. You can count on the failsafe system to act if higher-level modules fail. With braking in particular, maybe even a couple of redundant low-level emergency brake systems would be a good idea before you even consider any of the more high-level systems. You really don't want to hit jaywalking pedestrians or wandering drunks because both kinds do exist in reality. Similarly, once the car has a couple of obstacle-detection and auto-braking systems up and running, it's easier to work on autonomous driving because you can be confident that your computer won't be able to drive the car into anything as these isolated and separate systems will take care to stop the car. Consequently, when you're developing the navigation and routing system it has to be able to rely on the driving functions that deals with the present-time traffic situations, like keeping up with the flow of traffic, slowing down, changing lanes, etc. Again, same thing as with emergency brakes: to develop a smarter higher-level system you need to have lower-level failsafes in place. In the case of autonomous driving a failure should mean a harsh but unnecessary full stop or the inability to continue, not a collision or the inability to stop. They should definitely have left Volvo's own system on as an additional failsafe mechanism.