Can A Circle Of Salt Paralyze A Self-Driving Car?

Artist James Bridle demonstrated how a ritual-like trap could defeat an autonomous vehicle army.


Rachael Funnell


Rachael Funnell

Digital Content Producer

Rachael is a writer and digital content producer at IFLScience with a Zoology degree from the University of Southampton, UK, and a nose for novelty animal stories.

Digital Content Producer

salt circle self-driving car
Apparently circles and traffic cones are an autonomous vehicle's arch nemeses. Image credit: Taras Vyshnya / / IFLScience

Self-driving cars are within humans’ grasp – but as fans of science fiction, our brains can’t help but wonder whether the apocalypse will arrive in the form of a fleet of VW Beetles pursuing human prey across the desolate landscape that was once London free from an autonomous vehicle overlord. It is, of course, not going to happen, but the good news is that if it did, it seems a simple household seasoning could be our savior.

In 2017, artist James Bridle demonstrated how salt and an understanding of road markings could paralyze an autonomous vehicle by delivering conflicting messages. Two rings of salt around the vehicle, one in broken strips while the other is a block line, simultaneously tell it to go right ahead and not to cross. The result? Autonomous Trap 001.


The fun technological quirk is one that future models may be able to overcome, but it raises valid questions about the possibility of people manipulating the environment in a way that could disrupt a self-driving car’s capacity to drive itself. As it happens, conducting the experiment came with its own unique challenges, too.

“I ran out of salt, and had to drive back to the nearest village to buy a few more kilos,” Bridle told Vice. “Luckily, salt, unlike bandwidth and computational power, is a pretty cheap resource. Also, I should have pulled my trousers up for the video.”

The trap apparently caught the attention of newly-appointed Twitter CEO, Elon Musk, who also dabbles in autonomous vehicles. Responding to a now-suspended account Tweeting about the salt circle, Musk replied, "Probably will trap a Tesla with the production Autopilot build, but won’t work with [Full Self-Driving Capabilities]. Using a ring of cones would stop FSD though."

Sabotaging salt circles aside, there have been some other downsides to self-driving cars raised in recent years. Research has found that systems used in self-driving cars aren’t always very good at spotting darker skin tones, meaning a person’s chances of getting run over by one could be higher if they’re Black.


For people feeling anxious about a self-driving car’s capacity to spot them, in Japan, giant googly eyes were trialed as an indicator of the autonomous vehicle visual field.

“If the car is not looking at the pedestrian, this implies that the car does not recognize the pedestrian,” wrote the study authors. “Thus, pedestrians can judge that they should not cross the street, thereby avoiding potential traffic accidents.”

Looking like Brum 2.0, the design aims to provide anthropomorphic comfort to pedestrians, but we can’t help but feel that at night the eyes might take a rather more predatory turn.

Then again, if in doubt, simply get your salt and traffic cones out.


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