The federal government is upgrading its investigation into over a dozen incidents of Tesla vehicles using Autopilot that crashed into emergency vehicles. The probe is now designated as an “Engineering Analysis,” which is the second and final phase of an investigation before a possible recall.

This next phase will involve additional tests and crash analyses “to explore the degree to which Autopilot and associated Tesla systems may exacerbate human factors or behavioral safety risks by undermining the effectiveness of the driver’s supervision,” the National Highway Traffic Safety Administration (NHTSA) said in documents posted on its website Thursday.

The NHTSA is also expanding the number of Tesla vehicles that could be affected by the investigation, from 765,000 to 830,000. The probe covers Tesla Models S, X, 3, and Y vehicles that were released from 2014 through 2021.

The agency is looking into 16 crashes in which Tesla owners using Autopilot crashed into stationary emergency vehicles, resulting in 15 injuries and one fatality. Most of these incidents took place after dark, with the software ignoring scene control measures including warning lights, flares, cones, and an illuminated arrow board.

The investigation was first launched in August 2021. Since then, the NHTSA has solicited information from Tesla as well as 12 other automakers regarding their Level 2 driver assist systems, in which the vehicle can simultaneously control steering, braking, and acceleration on specific road types.

The agency is seeking data on miles driven as well as crash reports. Separately, the NHTSA is also collecting crash data from a broader group of companies that manufacture driver assist systems and fully autonomous vehicles.

In its preliminary report, the NHTSA said that the majority of crashes involved emergency vehicles that would have been visible to the driver on average eight seconds prior to the crash. “On average in these crashes, Autopilot aborted vehicle control less than one second prior to the first impact,” the agency reports.

Read the full report here: