Except this is a prototype, not a final product. Were a self driving car being made for public use, there would not be a pre-existing safety system to bypass or

Except this is a prototype, not a final product. Were a self driving car being made for public use, there would not be a pre-existing safety system to bypass or modify; it would be built in, or at the very least, the car would be delivered for modification with that system already removed. If you had a firewall in your network, for example, that had both a firewall system that you configured, and alongside it, a firewall configured by a third party with "best practices" in mind, that would be frustrating to configure and test because you'd never know for sure if it was a configuration you didn't setup correctly, or if it was this other firewall that you couldn't operate interfering with whatever it was you were doing. When designing things like this, step 1 is you remove variables that could change the behavior of the device in question without you knowing why it did. I'm sure once completed, a self driving car system could well be made to interface with the safety systems otherwise present, or could be designed in such a way where they wouldn't conflict. When you're in the thick of building that system, however, an additional (and by your comment, not exactly predictable) system to contend with, that you have no access to, is going to be a pain in the rear.