Tesla Inc. defended the safety benefits of its advanced driver assistance system Autopilot and its Full Self-Driving (FSD) capability but acknowledged they require “constant monitoring and attention of the driver.”

Democratic Senators Richard Blumenthal and Ed Markey wrote Tesla Chief Executive Elon Musk on Feb. 8 raising “significant concerns” about the electric-car maker’s Autopilot and FSD systems, which have prompted scrutiny from safety regulators.

In a previously unreported March 4 letter to the senators, Tesla’s senior director, public policy and business development, Rohan Patel, said the features enhance the ability of its customers “to drive safer than the average driver in the U.S.”

Patel noted that both systems “require the constant monitoring and attention of the driver.” Tesla vehicles are capable of performing “some but not all of the Dynamic Driving Tasks” that can be performed by human drivers, he added.

Tesla says on its website that Autopilot enables vehicles to steer, accelerate and brake automatically and “require active driver supervision and do not make the vehicle autonomous.”

Blumenthal and Markey said in a statement to Reuters the letter was “just more evasion and deflection from Tesla. Despite its troubling safety track record and deadly crashes, the company seemingly wants to carry on with business as usual.”

Tesla did not respond to a request for comment.

Patel said in the letter that Tesla “understands the importance of educating owners on the capabilities of Autopilot and FSD Capability.”

Autopilot allows drivers to keep their hands off the wheel at times, but Patel said its torque-based hands-on-wheel detection helps ensure drivers remain attentive.

Tesla launched a test version of its FSD system more than a year ago, enabling its vehicles to navigate city streets. Tesla has expanded the FSD deployment to 60,000 users, sparking criticism that it is risking safety by testing its technology with untrained drivers on public roads.

The automaker faces a number of investigations. The senators said in their letter the “complaints and investigations paint a troubling picture: Tesla repeatedly releases software without fully considering its risks and implications, creating grave dangers for all on the roads.”

Under pressure from regulators, Tesla in January agreed to recall about 54,000 U.S. vehicles to revise software to prevent vehicles from disregarding stop signs.

(Reporting by David Shepardson; additional reporting by Hyunjoo Jin in San Francisco; editing by Richard Pullin)