What should be passed (but I can't see how) is a percentage of allowed deaths, at least in the early years, and set it to something like 5-10% of the current rate, reducing downwards to 1% after 20 years.
People will die from self driving cars, and undoubtably their will eventually be a case that is 100% the self driving car's fault. The benefit of self driving cars comes from the mistake being permanently fixed, while with human drivers it can be committed over and over again.
There needs to be some kind of protection on the companies (and obviously the developers, I've never heard someone try to say they should be held responsible before) from lawsuits. Otherwise all it'll take a is a small handful beefore companies will just let it die.