Self-driving cars are safer by their very nature, since they avoid the mistakes of human drivers. However, that improved safety may create some new problems -- at least, according to MakerBot founder Bre Pettis. He tells Fortune that scientists will likely have to step up work on 3D-printed organs if and when robotic vehicles take off, since a significant chunk of organ donations (which are already scarce) come from car accident victims. Pettis isn't disputing the value of reducing road fatalities, of course. The issue is more that hospitals have to be ready for possible shortfalls in natural transplants.