By David Shepardson and Deborah Mary Sophia

WASHINGTON (Reuters) - Alphabet's Waymo is recalling more than 1,200 self-driving vehicles to update software and address risks of collisions with chains, gates and other roadway barriers after U.S. auto safety investigators opened a probe last year.

The recall affects 1,212 Waymo vehicles operating on the company's fifth-generation automated driving system software, the company said.

Waymo has over 1,500 vehicles on the road across San Francisco, Los Angeles, Phoenix and Austin, Texas, and is running more than 250,000 fully autonomous paid rides a week. It plans to add service in Atlanta, Miami and Washington, D.C.

Waymo said it was aware of 16 collisions with chains, gates and other barriers between 2022 and late 2024. But the incidents did not result in any injuries, according to a report filed with the National Highway Traffic Safety Administration.

NHTSA opened an investigation into the performance of Waymo self-driving vehicles in May 2024 after reports of its robotaxis exhibiting driving behavior that potentially violated traffic safety laws.

The agency said several incidents under investigation "involved collisions with clearly visible objects that a competent driver would be expected to avoid." The investigation remains open.

The issue has been resolved with a software update to its automated driving system begun in November and deployed across the entire fleet by the end of December, Waymo said.

"Waymo provides more than 250,000 paid trips every week in some of the most challenging driving environments in the U.S.," the company said on Wednesday. 

"Our record of reducing injuries over tens of millions of fully autonomous miles driven shows our technology is making roads safer," it added.

In February 2024, Waymo recalled 444 self-driving vehicles after two minor collisions in quick succession in Arizona, saying a software error could result in automated vehicles inaccurately predicting the movement of a towed vehicle.

Alphabet shares were up 4% on Wednesday.

Self-driving vehicle companies, including Waymo and General Motors' Cruise, have come under increased regulatory scrutiny following a 2023 incident where a pedestrian was seriously injured by a Cruise vehicle. GM cut Cruise's funding and folded it into its broader operations.

Waymo recalled more than 670 vehicles in June after one of them struck a wooden utility pole in Phoenix in May 2024. The company said the automated driving software could fail to avoid a pole or similar object.

Last week, Amazon.com's self-driving unit, Zoox, agreed to recall 270 driverless vehicles after an unoccupied robotaxi was involved in a crash with a passenger car in Las Vegas, Nevada. No one was injured.

(Reporting by Deborah Sophia in Bengaluru and David Shepardson in Washington; Editing by Anil D'Silva, Joe Bavier and Matthew Lewis)