Tesla declined to comment for this article.
The Autopilot update coincides with new policy guidelines for self-driving vehicles that the federal government issued this week. That policy, still subject to public review, gives the auto industry remarkable leeway in developing technology for fully autonomous vehicles. The main condition is that anything introduced for public use must be safe.
The policy guidelines do raise concerns about semiautonomous systems that â like Autopilot â are designed to perform many of the driving duties but still require human drivers to stay alert and be ready to take control at a momentâs notice. Otherwise, the technology could be considered âan unreasonable risk to safety and subject to recall.â
Anthony Foxx, secretary of transportation, said at a news conference this week that the new guidelines were not aimed at Tesla. But the National Highway Traffic Safety Administration is still investigating the Florida accident.
The question now is how just how new and improved Autopilot actually is â and whether a software download is sufficient to address what Teslaâs many critics say are the inherent shortcomings of the autonomous driving system.
One of those perceived drawbacks is Autopilotâs assumption that an attentive driver can and will take over control of the car in the event of an emergency. Researchers at other companies at work on self-driving cars â including Ford Motor and Google â have concluded that this so-called handoff can never happen quickly enough to be fully safe.
After Joshua Brown, 40, of Canton, Ohio, was killed driving a Tesla Model S in the first fatality involving a self-driving car, questions have arisen about the safety of the carâs technology.
A driver reviewing the updated Autopilot for The New York Times said the system required his full attention and he mentioned at least one occasion in which he would have had a collision had he not been poised to immediately hit the brakes.
The new Tesla software, called Version 8.0, also makes a significant change to the way Autopilot scans the road and recognizes objects. The previous version depended heavily on the forward-looking camera to sense surroundings. In the fatal Florida collision, the camera did not see a white tractor-trailer against a bright sky.
The new version of Autopilot relies more heavily on the carâs radar to identify other vehicles and potential obstacles, and to decide when to steer to avoid a problem or apply the brakes.
The elevation of radar might seem a modest difference. But it runs counter to the widely held view that radar, while highly accurate in measuring distance, is less precise in determining the shape and size of objects.
âIâm not completely sure how Tesla is able to recognize and classify objectsâ with radar, said Jeremy Carlson, a senior automotive analyst at the forecaster IHS Markit. âI think itâs clear there are changes in the new software in the radar sensor that are doing something in a very different way.â
Other automakers argue that cameras are better at recognizing and classifying objects.
âRadar is good at telling the distance to an object but not very good at recognizing what it is,â said Hideki Hada, general manager of Toyota Motorâs integrated vehicle systems group in Ann Arbor, Mich. âCameras can tell what an object is, but itâs not so good at telling the distance. So you need both.â
Despite their multitude of sensors and processors, autonomous cars have a lot of trouble with some everyday aspects of driving.
Companies at work on fully self-driving cars contend that conventional cameras and radar are not sufficient to enable a vehicle to sense and respond to its surroundings. They plan to incorporate an additional technology: a laser-powered type of radar called lidar.
Tesla argues that its current technology is adequate for Autopilotâs purposes. But in a Sept. 11 conference call announcing the upgrade, Mr. Musk acknowledged the challenge of using radar to identify objects.
The world, he said, looks âweirdâ in radar. Metal objects, because they strongly reflect radar waves, can appear larger than they are. Wood and plastic can appear âas transparent as glass.â Radar sensors tend to give âfalse positivesâ â instances when they think the car should brake when it actually doesnât need to.
The new Autopilot software has algorithms to adjust for radarâs distortions, according to Mr. Musk. And if the radar sees a large, dense, metal object â like a truck â the radar sensor can slow or brake the car, even if the camera system canât identify the object, he said.
Mr. Musk predicted that the new Autopilot system was âreally going to be beyond what people expectâ and would make the Tesla Model S sedan and the Model X sport utility vehicle âby farâ the safest cars on the road.
Mr. Ramsey, the research director at Gartner, noted that Tesla was able to release Autopilot last year without having committed to a crucial engineering question â Is the radar or the camera the primary sensor? â knowing the company could modify and improve it later.
âThey can take a risk like that,â he said. âItâs what makes them truly distinct from other automakers.â
Whether public experiments are the best approach to highway safety is another matter. âIâm sure they are very confident the cars are safe,â Mr. Ramsey said, âbut they are kind of doing trial and error.â