Uber Technologies Inc.’s self-driving system detected the woman who was struck and killed by one of the company’s autonomous vehicles in March, but the car’s automatic braking system was disabled, according to federal safety investigators.

The car’s radar and lidar sensors observed the pedestrian about six seconds before impact, according to a preliminary report about the incident released Thursday by the National Transportation Safety Board. The report does not establish probable cause of the collision.

Elaine Herzberg, 49, who was walking her bicycle across the street in Tempe, Arizona, was identified by the sensors first as an unknown object, then as a vehicle and then as a bicycle, the NTSB said. At 1.3 seconds before impact, the system recognized that emergency braking was needed, but Uber disables Volvo’s automatic emergency braking system in its SUVs while in autonomous mode to “reduce the potential for erratic behavior,” the NTSB said, citing the company.

“The vehicle operator is relied on to intervene and take action,” the NTSB wrote in the report. “The system is not designed to alert the operator.”

The crash has been a closely watched bellwether for the safety of autonomous cars in development and being tested on streets in multiple states. Uber permanently shut down its self-driving testing in Arizona Wednesday, before the release of the NTSB’s findings.