An autonomous, or self-driving, vehicle is defined by the University of Michigan Center for Sustainable Systems as one that uses “technology to partially or entirely replace the human driver in navigating a vehicle from an origin to a destination while avoiding road hazards and responding to traffic conditions.”The terms “autonomous” and “self-driving cars” are often used interchangeably.Two decades ago, the US military kicked off the race to build a self-driving car by sending a fleet of fledgling robot vehicles across the Mojave Desert in its seminal Darpa challenge.Ten years later, the auto industry was buzzing with predictions that self-driving cars would be all over the roads by now.That hasn’t happened. But the industry has started to put limited bits of automation, such as hands-free driving and crash-avoidance systems, into mass-produced models.And although a few companies are making progress toward fully autonomous vehicles — Alphabet’s Waymo recently expanded its robotaxi service to a third major US city — others have abandoned the technology, citing excessive costs and complexity.The industry had a rough 2023.General Motors’ self-driving Cruise unit suffered the most notable setback in October, when one of its robotaxis struck a pedestrian in San Francisco. As an alternatives to full autonomy, advanced driver-assistance systems — known as ADAS — help drivers park, stay in their lane and avoid objects using cameras, radar and other electronic sensors. They can alert drivers and in some cases briefly take control of the car to avoid collisions.The industry categorises automation systems from Level 0 to 5. Level 0 features simply pass on information to the driver, like sounding a warning when you’re driving out of a traffic lane.Tesla’s Autopilot is classified as Level 2 because it requires constant driver input and supervision, much in the way a pilot oversees certain automated systems in an airplane cockpit.Mercedes-Benz is offering Level 3 autonomy — which requires neither hands on the steering wheel nor eyes on the road — in select vehicles under certain conditions in parts of Germany and the US.Robotaxis that are being tested in confined areas in the US and China could be categorised as more advanced Level 4 systems, but these vehicles are limited in terms of where they can go.The pinnacle — which has yet to be achieved — would be Level 5 cars that can drive autonomously everywhere and in all conditions.Fatal crashes involving ADAS attract a lot of attention, especially if Tesla is involved. The US National Highway Traffic Safety Administration has opened dozens of investigations into crashes involving ADAS since 2016, most of them involving Teslas.Ford Motor and Volkswagen shut down their self-driving business Argo AI in October 2022, a dramatic turn of events for a business that had more than 2,000 workers and for a time was considering an initial public offering.Apple sank billions into trying to develop a vehicle with Level 4 or even Level 5 capability before deciding in February to shut down its car project. The National Highway Traffic Safety Administration initiated two probes just last week into Waymo and Zoox, the driverless technology subsidiaries of Alphabet Inc and Amazon.com.The investigations point to a more hands-on approach by a regulator that’s been relatively forbearing of automated-driving systems until recently.There’s still hope for the industry in 2024: Technology leaders such as Waymo and China’s Baidu are expanding services to new cities. In Texas, Aurora Innovation, Kodiak Robotics and Gatik AI expect to dispatch autonomous trucks by the end of the year, ditching human safety drivers after years of testing.China has been a hotbed of innovation thanks to dozens of startups and robust regulatory support.