Elon Musk explains it in this answer to Senator Shelby. The whole committe hearing is interesting, but your specific question is answered at 53:02 in the video,

Elon Musk explains it in this answer to Senator Shelby. The whole committe hearing is interesting, but your specific question is answered at 53:02 in the video, which I link here: https://www.youtube.com/watch?v=O_azyt1JhI0#t=3182 https://www.youtube.com/watch?v=O_azyt1JhI0#t=3182