Liability to some extent depends on the jurisdiction. For example, Washington DC will require drivers of autonomous-capable cars to get a special license endorsement and assume legal responsibility for the operation of the vehicle regardless of whether it is in autonomous mode or not. Presumably a driver who incurred legal liability for an accident while in autonomous mode would then turn around and seek damages from the vehicle and automation services provider as a separate action. For a completely autonomous vehicle (eg a bus or delivery van) the victim would likely recover from the corporate operator, who would probably not be using COTS technology anyway (think how UPS has its own trucks, or buses are often built to order for transit agencies).
The federal body (National Highway Transportation and Safety Board) seems to focused primarily on the development of technical standards that will allow for a uniform certification. But questions of driver liability will likely be left to the states, as most accidents resulting in lawsuits are tort actions alleging driver negligence, and different states have different rules on both driving and allocation of fault.
http://dcist.com/2014/04/dc_preparing_for_terrifying_future....
This page is a hub for legal information regarding autonomous vehicles: http://cyberlaw.stanford.edu/wiki/index.php/Automated_Drivin...
The federal body (National Highway Transportation and Safety Board) seems to focused primarily on the development of technical standards that will allow for a uniform certification. But questions of driver liability will likely be left to the states, as most accidents resulting in lawsuits are tort actions alleging driver negligence, and different states have different rules on both driving and allocation of fault.