an automated truck doesn't mean a driverless truck. it means the driver can be sleeping/tweeting/whatever during the boring hours between checkpoints/stops.
The levels overlap and vary by environment. Your truck can be level 5 on long stretch of highway, but then ring alarm bells and (if necessary, if the driver does not take over) slow down to a graceful stop on the shoulder before exiting the highway or maneuvering through a checkpoint or delivery.