As for the evaluation period for drivers who want to sign up, Tesla posted its “safety score” system on its website shortly before the button’s release. It said drivers would be scored on a 0 to 100 criteria, with most receiving 80 or above. Drivers will be assessed on five factors, it said: forward collision warnings per 1,000 miles, instances of hard braking, aggressive turning, unsafe following and forced disengagements of the Autopilot system. Tesla would then use a formula to calculate their score.