In the United States, the National Highway Traffic Safety Administration released its Preliminary Statement of Policy Concerning Automated Vehicles and it defined autonomous vehicle in five levels on 2013 (“U.S. Department,” 2013):
No-Automation (Level 0): The vehicle completely controlled by driver.
Function-specific Automation (Level 1): The vehicle has specific automation functions, such as electronic stability control or automatic braking.
Combined Function Automation (Level 2): The vehicle contains at least two controls can be automated in unison,