Following a fatal Model S crash on Autopilot reported earlier this week, one of Tesla’s main supplier for the Autopilot program, Mobileye, commented on the accident and explained that its Automatic Emergency Braking (AEB) wasn’t meant to avoid the impact.

Tesla has since responded to Mobileye’s statement, which we added to our article on the comment, but it’s worth elaborating on the differences between the systems as we recently learned more about them through tests earlier this week, and the tragic accident which is only now coming to light.

First of, here’s the statement issued by Dan Galves, Mobileye’s Chief Communications Officer:

“We have read the account of what happened in this case. Today’s collision avoidance technology, or Automatic Emergency Braking (AEB) is defined as rear-end collision avoidance, and is designed specifically for that. This incident involved a laterally crossing vehicle, which current-generation AEB systems are not designed to actuate upon. Mobileye systems will include Lateral Turn Across Path (LTAP) detection capabilities beginning in 2018, and the Euro NCAP safety ratings will include this beginning in 2020.”

Tesla quickly issued the following statement in response:

“Tesla’s autopilot system was designed in-house and uses a fusion of dozens of internally- and externally-developed component technologies to determine the proper course of action in a given scenario. Since January 2016, Autopilot activates automatic emergency braking in response to any interruption of the ground plane in the path of the vehicle that cross-checks against a consistent radar signature. In the case of this accident, the high, white side of the box truck, combined with a radar signature that would have looked very similar to an overhead sign, caused automatic braking not to fire.” What we learn here is that Mobileye’s system in Tesla’s Autopilot does gather the information from the vehicle’s sensors, primarily the front facing camera and radar, but while it gathers the data, Mobileye’s tech can’t (or not well enough until 2018) recognize the side of vehicles and therefore, itcan’t work in a situation where braking is required to stop a Tesla from hitting the side of another vehicle. Since Tesla pushed its 7.1 update earlier this year, the automaker’s own system used the same data to recognize anything, under adequate conditions, that could obstruct the path of the Tesla and if the radar’s reading is consistent with the data from the camera, it will apply the brakes. Now that’s something that was put to the test by Model S owners earlier in the week: In the last two tests, the Autopilot appears to detect an obstacle as evidenced by the forward collision warning alerts, but the automatic emergency braking didn’t activate, which raised questions – not unlike in the fatal crash. Though as Tesla explained, the trailer was not detected in the fatal crash, the radar confused it for an overhead sign, but in the tests above, the forward collision warning system sent out an alert – though as evidenced by the fact that the test subject wasn’t hit, the AEB didn’t need to activate and therefore it didn’t. Tesla explains: “AEB does not engage when an alternative collision avoidance strategy (e.g., driver steering) remains viable. Instead, when a collision threat is detected, forward collision warning alerts the driver to encourage them to take appropriate evasive action. AEB is a fallback safety feature that operates by design only at high levels of severity and should not be tested with live subjects.” It’s an efficient reminder that under the current system and until further improvements, nothing beats staying vigilant and always be ready to take action.

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