(Bloomberg) -- The top US auto-safety regulator expanded its investigation into Waymo, the autonomous-vehicle subsidiary of Alphabet Inc., after more incidents were identified in which the company’s cars were involved in collisions or may have violated traffic laws.

The US National Highway Traffic Safety Administration’s Office of Defects Investigation said in a letter to Waymo that it has identified nine additional incidents with similar patterns since it opened a preliminary evaluation on May 13. Reports indicate that 17 Waymo vehicles crashed into objects including gates, chains and parked cars. The agency also cited 5 instances in which the automated-driving system appeared to violate traffic rules, such as driving in opposing lanes with nearby oncoming traffic.

Read More: Alphabet’s Waymo Probed by US After Autonomous Car Incidents

NHTSA said in the letter, which is dated May 23 but was posted to the agency’s website on Friday, that some of the new incidents were reported by Waymo under a 2021 standing order that requires carmakers to inform regulators of any accidents involving automated driving systems. The agency said some of the other new incidents were identified by regulators who reviewed publicly available information. 

The defects office said it’s “concerned that ADS-equipped vehicles exhibiting such unexpected driving behaviors may increase the risk of crash, property damage, and injury.” 

Waymo didn’t immediately respond to a request for comment. 

Highway safety regulators have been subjecting both driver-assistance systems and more advanced autonomous vehicles to greater scrutiny. In addition to the ongoing Waymo investigation, probes have recently been launched into Tesla Inc.’s Autopilot, Ford Motor Co.’s BlueCruise and Amazon.com Inc.’s Zoox. 

The NHTSA also opened an investigation in October of possible defects in the automated-driving system developed by General Motors Co.’s self-driving unit, Cruise, which reached a settlement of more than $8 million after one of its vehicles hit and then dragged a pedestrian. 

Read More: Self-Driving Car Investigations Surge After Crashes and Mishaps

--With assistance from Bill Haubert.

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