Exported from the land of science fiction, some say the self-driving car remains a distant dream; others claim that several cars on the market today have surpassed the benchmark of ‘self-driving’. This polarization in opinion can arise from how one defines self-driving or autonomous car. To eliminate such confusions, SAE International has standardized the classification of autonomous vehicles using a 6-level system. 
Starting at Level 0 the car has zero automation and the human driver is in full control of all driving tasks. 
Level 1 vehicles can offer driver assistance in a specific function like steering or accelerating/decelerating.  The 2015 Toyota Camry XLE, which comes with adaptive cruise control but does not offer any additional features like lane-keeping, would classify as a Level 1 automated vehicle. 
Level 2 vehicles are partially automated and equipped with multiple driver assistance systems. However, the human driver is always expected to remain in control of the vehicle.  An example would be the Tesla Model S which can keep within a lane, automatically change lanes without requiring driver input and self-park with the expectation the driver is in control of the car. 
Level 3 vehicles take control of all aspects of the dynamic driving task, only requiring human intervention as a fallback. 
Level 4 vehicles are highly automated and can be driven unmanned. However, operation of the vehicles is constrained by environmental conditions.  In October 2015, Google’s self-driving prototype (outfitted with no steering wheel or foot pedal and with no test driver on board) carried Steve Mahan, a legally blind man, on the world’s first self-driving trip on public roads.  With Google’s software completely in control, this prototype can be categorized as a Level 4 vehicle. Since the vehicle was designed to self-drive only in relatively controlled environments, it does not classify as a Level 5 vehicle.
A Level 5 vehicle is characterized by a full-time automated driving system that can operate, requiring no human intervention, under all road and weather conditions. 
Regarding safety, it is worthwhile to note that autonomous vehicles such as Google’s prototype are driven over millions of miles on test tracks and in simulated driving before launching on a public road. On test tracks, performance is also tested in thousands of unique scenarios. 
Autonomous vehicles have the potential to revolutionize transportation on Earth and have a tremendous impact on space exploration. Improving automated navigation will allow rovers to explore distant planets more extensively. On Earth, autonomous vehicles can help to eliminate traffic accidents caused by human error, and reduce traffic congestion.  They also open the possibility of designing cars for people with visual or motor impairments, enhancing mobility for these marginalized groups.
Science fiction or reality, autonomous vehicles are on their way. Requiring a little push, i.e. continued research efforts, they will soon be driving themselves.
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