Waymo robotaxis wait to go into action.JasonDoiy/Getty Images The Alphabet Inc. unit, which operates its commercial ride service in three major cities and is adding a fourth, is starting to generate significant revenue. But safety concerns persist. By Alan Ohnsman, Forbes Staff Every week, hundreds of Phoenix, San Francisco and Los Angeles residents find a cheerful message in their email inboxes: “Buckle up! You’re ready to ride. Welcome to Waymo One. Get ready for your first fully autonomous ri...