New tests of automatic braking systems found a worrying flaw — and 2 Tesla models did the worst

• Five cars with automatic braking systems were stress-tested by the Insurance Institute for Highway Safety, a research group.
• One test found that Tesla’s Model 3 and Model S vehicles performed the worst, behind a BMW, a Volvo, and a Mercedes.
• The five cars were required to drive toward a stationary item with adaptive cruise control turned off and only automatic braking on.
• The two Teslas were the only cars that failed to stop in time and hit the object.
• In other parts of the test, the Teslas performed better and were even over-cautious when braking.

New tests of five cars’ automatic braking systems found some worrying problems with the technology, and two Tesla models were the worst performers.

The tests by the Insurance Institute for Highway Safety, a research group, found that some braking systems might not notice stopped vehicles and could even steer cars into a crash rather than away from it. It published the results in a Tuesday report.

In one test, the five cars drove at 31 mph toward a stationary object with the adaptive cruise control turned off and automatic braking on. The models all had automatic emergency braking systems deemed “superior” by the IIHS. They were:

• A 2017 BMW 5-Series with its “Driving Assistant Plus” function.
• A 2017 Mercedes-Benz E-Class with “Drive Pilot.”
• A 2018 Tesla Model 3 with Autopilot.
• A 2016 Model S with Autopilot.
• A 2018 Volvo S90 with Pilot Assist.

The stress test found that the Tesla Model 3 and Model S were the only two models that didn’t stop in time.

Both cars had braked and lessened the impact of a crash, but still hit the stationary item.

However, in a separate test with the adaptive cruise control turned on, the IIHS found that the Tesla models decelerated gradually and braked earlier than the other cars.

This occurred in a test simulating multiple cars driving in a row, where all the cars suddenly had to stop.

In fact, the IIHS noted that the Model 3 was prone to what it called “unnecessary or overly cautious braking.”

While travelling a distance of 180 miles, the car unexpectedly slowed down 12 times, seven of which after spotting tree shadows on the road, and the others for vehicles traveling toward it in another lane or crossing the road far ahead.

Jessica Jermakian, a senior research engineer at IIHS, said: “The braking events we observed didn’t create unsafe conditions because the decelerations were mild and short enough that the vehicle didn’t slow too much.

“However, unnecessary braking could pose crash risks in heavy traffic, especially if it’s more forceful.

“Plus, drivers who feel that their car brakes erratically may choose not to use adaptive cruise control” – which was turned off in the first test that the Teslas failed – “and would miss out on any safety benefit from the system.”

The Teslas performed the best when it came to staying within their lanes on curves and hills, however.

The IIHS in particular highlighted the fatal crash of a Tesla Model X in March as evidence of the shortcomings of driver assistance systems.

The car, which was driving while the semi-autonomous Autopilot software was engaged, crashed into a highway barrier in Mountain View, California, and caught fire. The driver, Walter Huang, died after being taken to the hospital.

Tesla later released a statement saying that Huang must not have been paying attention for the accident to take place, “despite the car providing multiple warnings to do so.”

The episode, the IIHS said, “demonstrates the operational limits of advanced driver assistance systems and the perils of trusting them to do all of the driving, even though they can’t.”

Tesla declined to comment.