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Highway Safety Tests Find Tesla Model S Has Some Trouble Staying in Its Lane

Tesla had a rough go at it in new highway safety tests recently conducted by the Insurance Institute for Highway Safety (IIHS).

The organization recently tested the Tesla Model S, Tesla Model 3, BMW 5 Series, Mercedes-Benz E-Class, and Volvo S90 on the safety of their adaptive cruise control and active lane-keeping performance. The agency specifically wanted to see how well the cars would avoid obstacles and stay within their lanes during simulated driving experiences. It then evaluated each of the vehicles based on how safely they performed during the rides.

In its testing, the IIHS set all of the cars to 31 miles per hour and pointed them at a stationary target. Cruise control was turned off, but autobrake was on to see whether the cars would stop before hitting a stationary target. Only the Tesla Model S and Model 3 hit the target. When the cruise control was turned on, however, the Teslas stopped before hitting the target.

All of the cars performed well in other cruise control tests, like when a lead vehicle slows down and then accelerates. Even when the cars could have hit a stationary target in the middle that was just 4.3 seconds away, all of the vehicles moved to avoid a collision.

In an active lane-keeping test, IIHS sent all of the cars along a road with curves and hills to see how they’d perform. A chart IIHS published shows a clear difference in the way the Tesla Model S performed compared to all the others—including the Model 3.

While Tesla’s Model 3 was able to stay in the line and only touched the line once when going over a hill, the Model S was a different story. That car went over the line once on curves and 12 times on hills.

“When cresting hills, the Model S swerved left and right until it determined the correct place in the lane, jolting test drivers,” IIHS said in a statement. “It rarely warned them to take over as it hunted for the lane center. The car regularly veered into the adjacent lanes or onto the shoulder.”

Of course, there’s much more than goes into the testing than meets the eye. And Tesla has been clear that its auto-steering feature in the Model S might not operate as well as it should on hills.

Tesla declined Fortune‘s request for comment on the tests.