Crash attenuators are designed to protect motorists by absorbing some of the energy generated by high-speed collisions with fixed objects, and the NTSB report points to the first of the two March 2018 wrecks as an example of their potential effectiveness.

The document says that on the night of March 12, a 31-year-old male driving a Toyota Prius southbound on U.S. 101 hit the intact attenuator at a speed "in excess of 75 mph." The driver, who was wearing his seat belt, survived with a broken finger and a small but potentially dangerous tear to one layer of his aorta.

The NTSB report says that a review of data from the Prius' event recorder showed that "the collision forces experienced by the Toyota driver were significantly lower than those resulting from the later (Tesla) crash with the damaged, nonoperational attenuator." That was due, the reports says, to the attenuator reducing the collision forces in the Toyota crash.

The safety board said that, in a breach of standard protocol, the CHP did not alert Caltrans that the crash device had been damaged. It wasn't until March 20, eight days after the Toyota crash, that a Caltrans maintenance crew happened across the location and advised a supervisor that a repair was needed.

The board report says the unidentified supervisor ordered the crew to place cones and a barricade at the site until repairs could be made. But staffing issues, bad weather and bureaucratic delays got in the way of a quick repair.

"The maintenance supervisor told the NTSB that staffing shortages, other necessary repair work, and 12-hour storm patrol shifts that were required on March 21 and 22 delayed the immediate repair of the attenuator," the report says. "In addition, the supervisor did not have a replacement crash attenuator at the local maintenance facility and had to call other facilities to find one. When two crash attenuators were found at a neighboring Caltrans maintenance facility, the supervisor had to obtain higher management approval from Caltrans District 4 to install them at the crash location because they had been reserved for installation at other locations."

It wasn't until March 26, three days after Huang died, that the crash attenuator was replaced. Huang's family filed a lawsuit against Tesla and Caltrans earlier this year.

The report notes that crashes at the site are frequent, with at least five vehicles striking the attenuator there in the three years before the fatal 2018 crash – more than at any other left-exit location in the Bay Area.

At least one of those earlier crashes also involved a vehicle slamming into a non-operational crash device. In November 2015, Phiet Truong, 67, of San Jose, suffered fatal injuries after driving his Lexus sedan into the attenuator, which had been damaged 45 days earlier. Caltrans replaced the safety device a month after Truong was killed.

The NTSB said the repeated failures to promptly repair or replace the attenuators at the crash site violated a long list of Caltrans policies that are supposed to ensure the timely repair of traffic safety hardware.

The CHP did not respond immediately to a request for comment. Caltrans spokesman Matt Rocco issued a brief statement: "Safety remains Caltrans' top priority. We are in the process of reviewing today’s report in conjunction with the California State Transportation Agency to determine the next steps."

The CSTA is the parent organization for both Caltrans and the CHP.