Highway Accident Brief 19/07 details the results of the
NTSB’s investigation of the crash involving a Tesla Model S P85 and a Culver
City Fire Department 2006 Seagrave Fire Truck in the high-occupancy vehicle
lane of southbound Interstate 405. No one was injured as a result of the crash.
The response to a collision in the northbound freeway lanes 25 minutes
earlier left a California Highway Patrol vehicle parked on the left shoulder of
southbound I-405 and the Culver City Fire Department truck parked diagonally
across the southbound HOV lane. Emergency lights were active on both vehicles. The
Tesla, which had its “Autopilot” system engaged, was traveling in the HOV lane,
behind another vehicle. After the lead vehicle changed lanes to the
right, the Tesla remained in the HOV lane, accelerated and struck the rear of
the fire truck at a recorded speed of about 31 mph. A forward collision warning
alert occurred 0.49 seconds prior to impact but the automatic emergency braking
system did not engage. The driver’s hands were not detected on the steering
wheel during this sequence nor did the driver apply steering or braking prior
to impact.
Tesla’s “Autopilot” system includes Autosteer and Traffic-Aware Cruise
Control. Autosteer is a lane-keeping assist system that can only be engaged
after Traffic-Aware Cruise Control is activated. The Traffic-Aware Cruise
Control is an adaptive cruise control system that modifies speed based on
information from the camera and radar sensors. The Tesla Model S owner’s manual
contains numerous warnings about the limitations of Traffic-Aware Cruise
Control and warnings about Autosteer and the need for drivers to keep their
hands on the wheel.
The NTSB determined the probable cause for the crash was the Tesla
driver’s lack of response to the fire truck parked in his lane, due to his
inattention and overreliance on the car’s advanced driver assistance system;
the Tesla’s “Autopilot” design which permitted the driver to disengage from the
driving task; and the driver’s use of the system in ways inconsistent with
guidance and warnings from Tesla.
(This
NTSB graphic depicts periods of manual and “Autopilot” control, with callouts
showing the percentage and duration of time the driver of a Tesla had his hands
off the steering wheel while “Autopilot” was engaged, for a Jan. 22, 2019, trip
that ended with a highway crash. NTSB graphic)
The NTSB’s investigation revealed the crash trip lasted
about 66 minutes, covering about 30 miles, with the “Autopilot” system engaged
for a total of 29 minutes, 4 seconds. Hands were detected on the Tesla’s
steering wheel for only 78 seconds of that 29-minute, 4-second period. For most
of the time the system was engaged, it did not detect driver -applied steering
wheel torque (hands on the steering wheel). The “Autopilot” system issued
several hands-off alerts during the last 13 minutes, 48 seconds prior to the
crash and was engaged continuously during those nearly 14 final minutes of the
crash trip. In the last 3 minutes, 41 seconds before the crash the system did
not detect driver-applied steering wheel torque.
During most of the driver’s operation with the “Autopilot” engaged, the
system detected and followed a lead vehicle, one that was ahead of the Tesla.
In the 15 seconds prior to the crash the system detected and followed two
different lead vehicles. Data show that 3 to 4 seconds before the crash, the
lead vehicle changed lanes to the right, a movement commonly referred to as a
“cut-out scenario” in testing and research. When the Traffic-Aware Cruise
Control no longer detected a lead vehicle, the system accelerated the Tesla
from about 21 mph toward the preset cruise speed of 80 mph, which had been set
by the driver about 5 minutes before the crash. The “Autopilot” system detected
a stationary object in the Tesla’s path about 0.49 seconds before the crash and
the forward collision warning activated, displaying a visual warning and
sounding an auditory warning. By the moment of impact, the Tesla had
accelerated to 30.9 mph.