Alphabet GOOGL.O self-driving unit Waymo on Tuesday defended its use of remote assistance personnel in the face of questions from Congress and said they have never been used to move robotaxis in U.S. on-road operations.

Waymo told Democratic Senator Ed Markey in a letter that it has not used remote driving or “tele-operations” to perform driving tasks. In rare circumstances, some U.S.-based personnel could prompt a stopped AV to move forward at 2 mph (3 kph) for a short distance to exit the travel lane but that has not happened outside of training.

Markey and Republican Representative Buddy Carter have raised concerns about the use of remote personnel including some remote assistance personnel based in the Philippines.

Waymo said its remote assistance personnel provide advice and support to Waymo robotaxis "but do not directly control, steer, or drive the vehicle."

Waymo operates four centers for remote assistance in Arizona, Michigan, and in two cities in the Philippines to support its fleet and at any given time, there are approximately 70 remote assistance agents, the company said. Only the Event Response Team, which manages responses to crashes or safety incidents and is based in the United States, could move a stopped vehicle.

Markey said in a February 3 letter that Waymo had provided little public information about its policies around remote personnel, adding Congress and the public deserve assurance that the company's remote assistance operations will not endanger passengers, other road users, or national security.

Markey sent other car companies similar letters including Tesla, Amazon.com's Zoox and Aurora.

Carter on Tuesday separately asked the Transportation Department to investigate Waymo's use of remote vehicle operators located in the Philippines, saying it "raises serious and reasonable concerns about roadway safety, situational awareness, and national security." USDOT said it would respond to Carter.

Waymo said remote assistance personnel "are not passively monitoring a vehicle or group of vehicles with the expectation to identify when intervention is needed" but the automated driving system reaches out when the vehicle encounters an ambiguous situation.

The Waymo robotaxi can also reject remote assistance suggestions if it deems it appropriate. "This distinction is fundamental to our safety model, ensuring the vehicle’s onboard system remains the primary, real-time authority for safe operation," Waymo said.

The average amount of time that elapses between a request for and delivery of advice is a matter of seconds and the car computer continues to make decisions independently based on all information available to it, Waymo said, adding that most of the time the robotaxi resolves its question on its own.

-David Shepardson/Reuters