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It is the first time that a production vehicle available to consumers will have such advanced self-driving capabilities. Or more to the point, the first time they will be unleashed for driving 70 miles per hour along twisty, though clearly marked, highways for long stretches. (Other manufacturers like Volvo and Mercedes-Benz recently introduced their own semiautonomous features, but limit the functions to lower speeds or require the driver to constantly touch the wheel.) And it’s perfectly legal. Among the states, only New York has any law prohibiting hands-free driving.

Thursday morning, Tesla owners woke up to discover that their vehicles can wirelessly download the new autopilot feature as a software update. That means the next time you see a Model S cruising next to you on the interstate, look closely: It may be driving itself.

Autopilot is not free (the download costs $2,500), and it is not yet perfected (clear lane markings are needed, and bad weather can affect its abilities), but it works remarkably well under normal circumstances.

The feeling of gliding autonomously through highway traffic initially feels a bit unnerving, especially on the Washington area’s notoriously congested roads. But on a recent afternoon while testing Tesla’s autopilot, that feeling faded as I began to trust the car to keep its lane along the twisty highway that hugs the Potomac River in Virginia.

One of the most soothing aspects of the system was how natural the steering felt through the turns. To mimic a human driver is one of the big challenges automakers face in designing self-driving cars. That is because computers can be so perfect that they may constantly adjust to stay exactly in the middle of a lane, resulting in a lot of little jerky motions of the wheel that feels unnatural. Not the Tesla. It was silky smooth.

That does not mean, of course, that drivers can simply relax and let their minds wander. The car is skilled at keeping its lane, but when lane markings disappear or are significantly faded, you have to take over.

Similarly, when heading through construction zones, or when traffic is merging, the human driver is wise to keep full control. If you are in the right lane of a highway and cars are merging at slower speeds, most drivers want to move over a lane and go around them. But the Tesla does not know that. It will instead automatically slow to match the slower speeds of the merging cars.

The autopilot does include an auto lane-change feature that allows a driver to switch lanes simply by using the turn signal. The car scans to make sure nobody is in the next lane and then moves over. So in theory, for highway merges, a driver could tell the Tesla to slide over and pass the slower cars. In practice on my recent test drive, I played it safe and took over control.

Tesla officials have stressed that ideally drivers should keep at least one hand on the wheel at all times. The company’s chief executive, Elon Musk, also said on Wednesday that the company considered autopilot still in “beta” and that drivers had to assume liability when they used it. In other words, if you go hands-free and get into an accident, Tesla says it is not going to pay the bill.

But in practice, while drivers need to stay alert, the system indeed allows for hands-free driving. On my drive through the southern end of Washington and into Virginia, I began by hovering my hands an inch or so above the wheel, just to get comfortable. After about 20 minutes, I found myself resting my hands on my lap.

If the system loses confidence in its ability to read the road ahead, however, either because of bad lane markings, weather issues or anything else, it signals the driver with a blue message on the dashboard, followed by audible alerts, indicating the driver needs to take the wheel. Ignore those sounds and the autopilot will disengage, bringing the vehicle to a stop.

Unlike other offerings on the market, however, those alerts are not on a timer. The car does not prompt you to place your hands on the wheel after a set period of time, Tesla said. So as long as the autopilot system is working properly and is confident in its road-scanning, drivers, as I did for long stretches this week, can let the Model S do the driving.

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