The March 23rd death of a Tesla Model X driver in Mountain View, California prompted the National Transportation Safety Board to probe why the vehicle, driving in Autopilot mode, left its lane and collided with a concrete lane barrier on a clear day. The impact killed 38-year-old Walter Huang, an Apple engineer.
In the wake of the crash, the safety agency booted Tesla from the investigation after the automaker released details relating to the vehicle’s (and victim’s) actions in the moments leading to the crash. We now have the NTSB’s preliminary report on what happened before, during, and after the collision.
As we detailed at the time, Huang’s Tesla was travelling southbound on US-101 in the high-occupancy vehicle (HOV) lane, approaching the State Highway 85 interchange. The exit lane was to Huang’s left approaching the split, and a paved gore area opens up between the two lanes as the SH-85 ramp branches off. According to the NTSB, Huang’s cruise control was set at 75 mph on the 65 mph roadway, with Autopilot functions (traffic-aware cruise control and autosteer lane-keeping) turned on four separate times during the 32-minute trip.
Autopilot was engaged for the last 18 minutes, 55 seconds of the journey.
“As the Tesla approached the paved gore area dividing the main travel lanes of US-101 from the SH-85 exit ramp, it moved to the left and entered the gore area,” the preliminary report states. “The Tesla continued traveling through the gore area and struck a previously damaged crash attenuator at a speed of about 71 mph.”
Here’s the NTSB’s breakdown of what occured before impact:
- The Autopilot system was engaged on four separate occasions during the 32-minute trip, including a continuous operation for the last 18 minutes 55 seconds prior to the crash.
- During the 18-minute 55-second segment, the vehicle provided two visual alerts and one auditory alert for the driver to place his hands on the steering wheel. These alerts were made more than 15 minutes prior to the crash.
- During the 60 seconds prior to the crash, the driver’s hands were detected on the steering wheel on three separate occasions, for a total of 34 seconds; for the last 6 seconds prior to the crash, the vehicle did not detect the driver’s hands on the steering wheel.
- At 8 seconds prior to the crash, the Tesla was following a lead vehicle and was traveling about 65 mph.
- At 7 seconds prior to the crash, the Tesla began a left steering movement while following a lead vehicle.
- At 4 seconds prior to the crash, the Tesla was no longer following a lead vehicle.
- At 3 seconds prior to the crash and up to the time of impact with the crash attenuator, the Tesla’s speed increased from 62 to 70.8 mph, with no precrash braking or evasive steering movement detected.
The NTSB’s finding that Huang did not have his hands on the wheel for the final six seconds jibes with what Tesla released shortly after the crash. The same goes for the audio and visual warnings.
As this is just a preliminary report, the NTSB isn’t saying why the Tesla’s autosteer moved the vehicle from the HOV lane, where it had slowed to match the speed of the lead vehicle. There’s video evidence, posted to YouTube from another Tesla driver, that suggests the poor condition of the solid white line separating the HOV lane from the gore area may have confused the vehicle’s lane-keeping system.
Once the Tesla moved into the gore area and away from the leading vehicle, it seems the vehicle’s traffic-aware cruise control attempted to accelerate the vehicle back up to its preset speed.
While bystanders removed Huang from the wreckage before his vehicle was consumed by flames, the car’s lithium-ion battery proved troublesome for firefighters long after the initial blaze was doused. Such batteries are highly volatile when breached, and extinguishing them often proves difficult.
Per the NTSB report, “Around 4:30 p.m. that afternoon, at the impound lot, the Tesla battery emanated smoke and audible venting. The battery was monitored with a thermal imaging camera, but no active fire operations were conducted. On March 28, 5 days after the crash, the battery reignited. The San Mateo Fire Department responded and extinguished the fire.”
That’s all we have to go on for now. “All aspects of the crash remain under investigation as the NTSB determines the probable cause,” the agency wrote, “with the intent of issuing safety recommendations to prevent similar crashes.”
[Image: Screencap, KGO-TV]