Google executive David Drummond left the Uber board of directors as competition revs up between the companies over self-driving cars. “I recently stepped down from Uber’s board given the overlap between the two companies,” Google chief legal officer Drummond said in a statement. Drummond noted that Google remains an “enthusiastic investor” in the on-demand ride-sharing service. Uber co-founder and chief executive Travis Kalanick said Drummond had been a “sage advisor and great personal friend,” and adding that he was looking forward to continued cooperation between the companies. Google parent Alphabet and San Francisco-based Uber have both been working on getting self-driving cars on roads, with their relationship evidently getting bumpier as efforts gain traction.