The US government's road safety agency is investigating Tesla's "Full Self-Driving" system after getting reports of crashes in low-visibility conditions, including one that killed a pedestrian.

The National Highway Traffic Safety Administration (NHTSA) said in documents that it opened the probe on Thursday, local time, after the company reported four crashes when Teslas encountered sun glare, fog and airborne dust.

In addition to the pedestrian's death, another crash involved an injury, the agency said.

Investigation to look into visibility conditions

Investigators will look into the ability of "Full Self-Driving" to "detect and respond appropriately to reduced roadway visibility conditions, and if so, the contributing circumstances for these crashes."

The investigation covers roughly 2.4 million Teslas from the 2016 through 2024 model years.

A message was left on Friday seeking comment from Tesla, which has repeatedly said the system cannot drive itself and human drivers must be ready to intervene at all times.

Last week, Tesla held an event at a Hollywood studio to unveil a fully autonomous robotaxi without a steering wheel or pedals. 

Robotaxis available from 2026

Chief executive Elon Musk, who has promised autonomous vehicles before, said the company plans to have autonomous Models Y and 3 running without human drivers next year. 

Robotaxis without steering wheels would be available in 2026 starting in California and Texas, he said.

The investigation's impact on Tesla's self-driving ambitions isn't clear. NHTSA would have to approve any robotaxi without pedals or a steering wheel, and it's unlikely that would happen while the investigation is in progress. 

But if the company tries to deploy autonomous vehicles in its existing models, that likely would fall to state regulations. There are no federal regulations specifically focused on autonomous vehicles, although they must meet broader safety rules.

NHTSA also said it would look into whether any other similar crashes involving "Full Self-Driving" have happened in low visibility conditions and it will seek information from the company on whether any updates affected the system's performance in those conditions.

"In particular, this review will assess the timing, purpose and capabilities of any such updates, as well as Tesla's assessment of their safety impact," the documents said.

Tesla reported the four crashes to NHTSA under an order from the agency covering all automakers. 

An agency database says the pedestrian was killed in Rimrock, Arizona, in November of 2023 after being hit by a 2021 Tesla Model Y. Rimrock 161 kilometres north of Phoenix, Arizona.

The Arizona Department of Public Safety said in a statement that the crash happened just after 5pm on November 27 on Interstate 17. Two vehicles collided on the freeway, blocking the left lane. 

A Toyota 4Runner stopped and two people got out to help with traffic control. A red Tesla Model Y then hit the 4Runner and one of the people who exited from it. 

A 71-year-old woman from Mesa, Arizona died at the scene.

The collision happened because the sun was in the Tesla driver's eyes, so the driver was not charged, said Raul Garcia, public information officer for the department. 

Sun glare also was a contributing factor in the first collision, he added.

Tesla has twice recalled "Full Self-Driving" under pressure from NHTSA, which in July sought information from law enforcement and the company after a Tesla using the system struck and killed a motorcyclist near Seattle.

The recalls were issued because the system was programmed to run stop signs at slow speeds and because the system disobeyed other traffic laws. Both problems were to be fixed with online software updates.

Critics say Tesla's system doesn't have proper sensors

They have said that Tesla's system, which uses only cameras to spot hazards, doesn't have proper sensors to be fully self driving. Nearly all other companies working on autonomous vehicles use radar and laser sensors in addition to cameras to see better in the dark or poor visibility conditions.

Mr Musk has said that humans drive with only eyesight, so cars should be able to drive with just cameras. He has called lidar (light detection and ranging), which uses lasers to detect objects, a "fool's errand."

The "Full Self-Driving" recalls arrived after a three-year investigation into Tesla's less-sophisticated Autopilot system crashing into emergency and other vehicles parked on highways, many with warning lights flashing.

That investigation was closed last April after the agency pressured Tesla into recalling its vehicles to bolster a weak system that made sure drivers are paying attention.

 A few weeks after the recall, NHTSA began investigating whether the recall was working.

NHTSA began its Autopilot crash investigation in 2021, after receiving 11 reports that Teslas that were using Autopilot struck parked emergency vehicles. 

In documents explaining why the investigation was ended, NHTSA said it found 467 crashes involving Autopilot resulting in 54 injuries and 14 deaths.

Autopilot is a fancy version of cruise control, while "Full Self-Driving" has been billed by Mr Musk as capable of driving without human intervention.

The investigation that was opened on Thursday enters new territory for NHTSA, which previously had viewed Tesla's systems as assisting drivers rather than driving themselves. 

With the new probe, the agency is focusing on the capabilities of "Full Self-Driving" rather than simply making sure drivers are paying attention.

Executive director of the nonprofit Center for Auto Safety Michael Brooks, said the previous investigation of Autopilot didn't look at why the Teslas weren't seeing and stopping for emergency vehicles.

"Before they were kind of putting the onus on the driver rather than the car," he said. 

"Here they're saying these systems are not capable of appropriately detecting safety hazards whether the drivers are paying attention or not."

AP