One problem is apparent from a casual glance at a prototype car: lidar sensors are bulky. They are why vehicles being tested by Waymo, Alphabet’s self-driving-car unit, are topped by a giant black dome, and Toyota’s and Uber’s sport spinning gadgets the size of a coffee can.  Lidar sensors are also expensive, costing thousands or even tens of thousands of dollars apiece. Most vehicles in testing have multiple lidars onboard, and despite the relatively small numbers on the road, demand has become a problem. The Information reported last week that lidar manufacturers are struggling to keep up, forcing companies to wait six months for a new sensor.