Two Waymo self-driving cars crashed into a pick-up truck being towed in Phoenix, Arizona, resulting in the company issuing a voluntary recall of its vehicles. 

According to Waymo, one of their cars 'incorrectly predicted the future motion', of a backward-facing pickup truck that was being 'improperly towed', and collided with it, causing no injuries and 'minor damage' to the car. 

A few minutes later another Waymo vehicle made contact with the same pickup while it was being towed in the same manner.

Waymo later discovered that its software had incorrectly predicted the future movements of the pickup truck due to 'persistent orientation mismatch' between the towed vehicle and the one towing it. The company developed a fix for its software which it deployed to its fleet through a 'recall'. 

The incident highlighted safety concerns about Waymo and about the self-driving car industry.