Automakers aren't doing enough to ensure that drivers are ready to take over if their vehicles' self-driving features make mistakes, a new advisory argues, re-igniting a debate about who should be held accountable when the drivers of partially automated cars kill people on U.S. roads.

Last week, the Insurance Institute for Highway Safety announced the criteria for a new set of rankings that will evaluate how well automakers are combatting "automation complacency" among their drivers, as well as the intentional misuse of advanced driver assistance systems that are becoming increasingly common on new cars.

"At some point, we have to ask ourselves: are these, indeed, driver safety systems?" said one expert. "Or are they driver convenience systems?"