You still have the driver in the driver’s seat, ready to take over at all times in case something goes wrong or the system encounters a situation it’s not really well prepared for,” says Alex Davies, associate editor for Wired, who was at the demonstration and rode in the big rig. The driver controls the rig on surface roads, but on the highway, engages the autopilot mode. Cameras detect the lane lines to keep the truck headed in the right direction, Davies tells NPR’s Rachel Martin.