A Tesla Mystery: Why Didn’t Auto Braking Stop These Accidents?

On a rainy winter night in December 2019, college student Maria Smith found herself being followed by a state agent, with flashing police lights, on Route 24 in Massachusetts. She stopped on the side of the road. Then: Slap! Something had hit her car from behind her, shattering her rear window. “I was scared,” she said she.

A Tesla in autopilot mode had crashed into the state police cruiser, causing it to fall into Smith’s car.

No one was injured, but it is part of a extensive investigation launched in August by the National Highway Traffic Safety Administration. NHTSA is reviewing a dozen similar incidents over three years in which Tesla vehicles traveling at a range of speeds bumped into stationary police cars, fire trucks, ambulances, and other emergency vehicles, injuring 17 people and killing one.

Announcing the probe, NHTSA noted that all Tesla vehicles involved operated on autopilot or traffic-sensitive cruise control, software systems that allow the driver to forgo speed control and sometimes to steer while, at least in theory, remaining ready to intervene. NHTSA She said it would examine factors such as how the vehicle makes sure drivers pay attention and how it detects visual cues of an accident scene such as flashing lights and flares, details that an alert human driver is unlikely to miss.

But its investigators will also analyze a question involving more basic technology: Why isn’t Tesla’s front collision avoidance system better at preventing accidents like Smith’s, at least when the computer is driving?

Compared to so-called advanced driver assistance systems such as autopilot, a forward collision avoidance system is relatively crude. It’s designed to answer a question: Is a frontal impact imminent? – and respond to the hazard by issuing a warning signal and, if necessary, by activating a subsystem called automatic emergency braking. Unlike the Autopilot, which must be manually selected and is only available in certain driving conditions, automatic emergency braking works by default unless it is manually deactivated.

First developed in the mid-1990s, automatic emergency braking is effective in preventing or reducing the severity of accidents, said David Aylor, head of active safety testing for the Insurance Institute for Highway Safety. The IIHS found that automatic braking systems can reduce the incidence of front-to-rear crashes by 50%, performing better at lower speeds and in good visibility.

“We think it’s great technology and all cars should have it,” Aylor said.

“The benefits are quite surprising,” said Kelly Funkhouser, head of connected and automated vehicles for Consumer Reports. “It’s the only technology without which I would never let a family member or friend buy a car.”

Tesla calls its vehicles “the safest cars in the world “ citing their combination of structural engineering and advanced technology. But when it comes to the front collision avoidance system, Tesla owners have reported problems at a substantially higher rate than similarly equipped cars.

In 2020 and the first three quarters of 2021, NHTSA received 131 complaints about Tesla’s system, compared with 55 for Mercedes-Benz, 28 for Audi and 14 for Volvo. Each of the four automakers standardized collision avoidance systems on all of its cars before the industry’s voluntary expiration at the end of next year.

Tesla’s complaint rate for the number of its cars sold in the United States in 2020 was more than three times that of other automakers.

Tesla does not have a media relations department, and chief executive Elon Musk did not respond to attempts to ask for comment.

The accident and complaint pattern is raising alarms among safety advocates and automotive tech pundits.

“The Teslas are encountering stationary objects,” said Alain Kornhauser, who heads the driverless automotive engineering program at Princeton University. “They shouldn’t be.” If the company’s cars can’t avoid accident scenes marked by flares or traffic cones, he said, “How can you trust anything else they do with Autopilot?”

In testing, the Tesla S, X and 3 models earned “top” ratings from the IIHS for their front collision avoidance systems. (Model Y has not yet been tested.) IIHS said 84 percent of all auto brake systems from all automakers have been given a superior designation.

But those tests are conducted at just 12 mph and 25 mph, according to Aylor. The IIHS does not perform the test at high speeds or with autopilot or similar systems activated.

In the operation manuals provided to Tesla owners, the company states that its automatic emergency braking is designed to operate at speeds between 3 mph and 90 mph. That language comes with several disclaimers, including the caveat that automatic braking is “designed to reduce the severity of an impact. It is not designed to avoid a collision.”

A 2020 relationship by the National Transportation Safety Board summarizing the investigation of four Tesla incidents highlighted “the limitations of [forward] Collision avoidance systems … when vehicles … are traveling at high speed or are confronted with shapes or objects in the vehicle that the system was not designed to detect. … Systems are not designed or tested to operate consistently at speeds above 50 mph.

Best known for its airline disaster probes, the NTSB has no regulatory authority, but its investigations have highlighted issues related to the development and performance of automated vehicles, including frontal collision avoidance.

In a fatal accident in Mountain View, California in 2018, an autopilot Tesla crashed head-on into a concrete pillar. NTSB determined that Tesla had not designed its system to avoid such road obstacles, according to its report. “As a result, the front collision warning system did not give a warning and the automatic emergency braking did not activate.”

Advanced Driver Assistance Terms

In a high-speed crash in Texas this year, a Tesla on autopilot mode caused a chain reaction that sent five state policemen to the hospital, according to court records. A plaintiff’s filing states that the car was traveling at 70 mph and “did not apply its ‘automatic emergency braking’ to slow down to avoid or mitigate the accident.” Tesla has not yet filed an answer to the lawsuit.

An NTSB report on a 2018 accident on Highway 405 in Culver City, in which an autopilot Tesla crashed into the back of a parked fire truck, said the NTSB determined that the car was traveling at 30.9 mph on impact. Not only did the automatic emergency braking fail to activate, but the car accelerated just before the collision, investigators said, from 21 mph.

This is the speed range where auto-braking emergency should excel, Aylor said.

Based on these findings, the board has since 2018 recommended that the NHTSA develop and apply tests to evaluate the performance of forward collision avoidance systems at various speeds, including high speeds. NHTSA hasn’t done so yet.

“NHTSA has taken no action to gain a better understanding of how these life-saving technologies perform in real-world high-speed crash scenarios,” the NTSB said in a report on how its recommendations were received.

Asked for comment, an NHTSA spokesperson said in a statement that the agency “continues to collect data and conduct research that will inform and be necessary precursors of several regulatory actions” on the agenda. The agency declined a request for an interview with an NHTSA official.

In its investigation of accidents involving emergency vehicles, the NHTSA appears to be intent on understanding the interaction between autopilot and automatic emergency braking and which one has brake control when an obstacle is detected. In an August 31 letter to Eddie Gates, Tesla’s director of field quality, the agency instructed him to describe the autopilot’s control over functions, including braking and acceleration “during routine operations and imminent in case of an accident “.

One possibility, according to Missy Cummings, a former Navy fighter pilot studying human-machine interaction at Duke University, is that the autopilot is designed to prevent or suppress emergency braking to minimize so-called phantom braking.

“I haven’t seen the code to tell how Tesla works, but I suspect the AEB is disabled in some situations,” he said. “If it were left on, it could detect what are called ghost objects and it would be hitting the brakes.”

Mahmood Hikmet, an autonomous vehicle research engineer in New Zealand, said that automatic emergency braking can interfere with testing of truly driverless systems, something Tesla is currently doing on a large scale with a public beta test of its so-called Full Self Driving software.

In 2018 a pedestrian crossing of the street was crossed killed from a self-driving Uber test car manufactured by Volvo. The automatic braking system had been disabled, according to Aptiv, which provided the system’s camera and radar. The vehicle security driver did not see the woman on the street at night and the car passed over her at highway speeds without stopping.

“You could disable some safety features to evaluate how the system you are testing works,” said Hikmet, but “ideally” on closed tracks with safety-savvy drivers and clear operating rules.

Maria Smith, for example, thinks there should be more clarity about how automated driving and safety systems work and why they sometimes don’t.

“Teslas are such great cars,” Smith said. “But they’re testing them with the rest of us out here driving our nerdy cars that don’t drive alone.”