This was discussed in several very interesting sessions at the (fabulous – thank you, Ryan Calo and Michael Froomkin among others!) We Robots 2013 conference a few weeks ago at Stanford Law School (there is video as well as the draft papers presented at the link)...The liability issue is under discussion in many quarters, of course, such as the special 2012 law review symposium of the Santa Clara University School of Law (which, given its location, has carved out an important role in these emerging technologies) on legal issues related to driverless cars.
More links:
http://www.templetons.com/brad/robocars/accident.html
http://www.volokh.com/2013/05/05/self-driving-vehicles-how-soon-and-who-will-bear-the-liability-costs/ with a potential pointer to more detailed legal work:
http://www.thedailybeast.com/articles/2013/01/24/are-driverless-cars-really-in-our-near-future.html
http://www.economist.com/news/special-report/21576224-one-day-every-car-may-come-invisible-chauffeur-look-no-hands
http://www.economist.com/news/business/21564821-carmakers-are-starting-take-autonomous-vehicles-seriously-other-businesses-should-too