XKCD on tricking self-driving cars: https://xkcd.com/1958/

I wanted to link that not because of the "there's an XKCD for everything" meme but because it makes an interesting point: sabotaging roads isn't difficult now, with human drivers. There's no reason to assume it would suddenly become a substantial threat when autonomous cars are commonly adopted. An issue worth considering and accounting for, but not worth public worry.