By David Shepardson
WASHINGTON (Reuters) -The U.S. National Highway Traffic Safety Administration said on Friday it is seeking more information in its investigation into Amazon.com (NASDAQ:AMZN)'s self-driving Zoox vehicles due to unexpected braking that led to two rear-end collisions.
The agency, which opened its probe into the crashes this month, said it is seeking video of the crashes and documents from Zoox related to the vehicles.
NHTSA said it "is concerned that vehicles exhibiting unexpected rapid braking may increase the risk of crash," and added the "risk is particularly acute to road users behind the Zoox vehicles who are unable to reasonably anticipate or react to the unexpected sudden braking."
NHTSA said earlier this month it had opened its "preliminary investigation of 500 Zoox vehicles with automated driving systems after two crashes involving the self-driving technology unit's vehicles equipped with the Zoox Automated Driving System that resulted in minor injuries to motorcyclists.
Each incident involved a Toyota (NYSE:TM) Highlander equipped with the automated driving system, which is being tested in the real world using those vehicles.
A Zoox spokesperson did not immediately comment on Friday but said earlier that "transparency and collaboration with regulators is of the utmost importance, and we remain committed to working closely with NHTSA to answer their questions."
In March, Zoox said it was expanding its vehicle testing in California and Nevada to include a wider area, higher speeds and nighttime driving, as it competes with Alphabet (NASDAQ:GOOGL)'s Waymo robotaxis. Amazon acquired Zoox in 2020 for $1.3 billion.
NHTSA said both crashes occurred during daytime and within the Zoox system's operational design limits.
The investigation will evaluate the automated driving system's performance, particularly relating to the collisions as well as "the behavior in crosswalks around vulnerable road users, and in other similar rear-end collision scenarios."
NHTSA in March 2023 opened a probe into Zoox's self-certification in 2022 of a robotaxi without traditional driving controls. Self-certification is a standard practice in the industry, but is subject to regulatory oversight.
NHTSA has opened a series of investigations into the performance of self-driving vehicles, including into General Motors (NYSE:GM)' Cruise and Alphabet's Waymo.
The agency is also investigating Tesla (NASDAQ:TSLA)'s December recall of more than 2 million vehicles to install new Autopilot software after NHTSA received reports of 20 crashes involving vehicles with the software update. Autopilot is an advanced driver assistance system that does not make vehicles fully self-driving but handles driving tasks like steering and braking.