The utility of the car metaphor is that both computers and cars have to work safely for non-professional users. Cars are overwhelmingly driven by people whose j

The utility of the car metaphor is that both computers and cars have to work safely for non-professional users. Cars are overwhelmingly driven by people whose job isn't to drive a car and computers are used by non-professional users all the time. This is a critical point, as it's a lot harder to enforce safety practices or education on people who don't have a professional obligation to follow those practices. You have to design your systems to work for people who will do everything wrong. In terms of mitigating severity from crashes, cars are far ahead of airplanes. Of course, air travel is a great area to draw on for security when it comes to professional computer users (developers, sysadmins, etc.). A lot of the practices which have improved safety in air travel (automation, checklists, blameless post mortems) are directly applicable to computing safety when it comes to people whose job it is.