(Chandler, AZ) -- Chandler police say someone has been vandalizing self-driving cars. They confirm there have been 21 attacks on Waymo's autonomous vehicles since they hit the road in 2017. Chandler police say they've been called for slashed tires, drivers trying to run Waymo cars off the road, and even weapons being pointed at Waymo back-up drivers. Waymo started testing its self driving vehicles in Chandler in 2017. Last month it officially launched its driverless taxi service.