Autonomous vehicles were supposed to cut traffic—what if they don't?

The age of robotaxis, long the preserve of science fiction, is now a reality, at least in a handful of American cities. It took just over a decade to get from the DARPA Grand Challenges to the start of Waymo's commercial service in California, albeit initially with a safety driver on board. Proponents of the technology, which has attracted at least $100 billion in investment, say robotaxis will be safer than human-driven vehicles.