Uber's self-driving cars are getting "bullied" by pedestrians and human drivers, the company's head of autonomous driving, Eric Meyhofer, said on Wednesday.

Meyhofer said people were "testing the boundaries of what they can do to self-driving" with rude gestures, forcing the cars to stop, and driving up close on their tails.

Google's autonomous-vehicle unit, Waymo, has experienced similar issues , with people slashing tires and even pulling guns on safety drivers.

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Spare a thought for Uber's driverless cars, which are apparently getting mercilessly bullied by pedestrians and other drivers while out on the road.

That's according to Eric Meyhofer, the head of Uber's self-driving car unit, Advanced Technologies Group. Speaking at the Elevate conference in Washington, DC, on Wednesday, he said cameras mounted on the vehicles were capturing the hostility.

"We've seen people bully these cars — they feel like they can be more aggressive because we won't take a position on it, or we'll allow it," Meyhofer said, according to The Daily Telegraph.

"You're on video but still people do bully them, and that's a fascinating thing to see where people are testing the boundaries of what they can do to self-driving," he added.

Read more: An engineer at Uber's self-driving-car unit warns that it's more like 'a science experiment' than a real car capable of driving itself

According to Meyhofer, the bullying comes from both pedestrians and other road users. It takes the form of rude gestures and utterances, challenging the cars to brake, driving up close behind them, and tending not to give the cars right of way at junctions. Meyhofer called the behavior "mean-spirited."

A Waymo car. Getty

This isn't the first time human hostility toward autonomous vehicles has been documented. The Arizona Republic reported last year that people were slashing the tires of vehicles owned by Waymo, Google's self-driving-car venture. Guns were also pulled on safety drivers, it was reported.

Uber's self-driving-car program restarted in December after being suspended for nine months following a fatal crash that killed a pedestrian.