I think you will see pilotless planes long before completely driverless cars gain any popularity, because of the problem of human-automation handoff latency.
In planes, when the autopilot disconnects because of some problem there's usually plenty of warning (including a sound like https://www.youtube.com/watch?v=8XxEFFX586k ) and the pilot(s) have some time, seconds or more, to assess the situation and take control. Despite how fast planes fly, the rules of separation and general vastness of airspace make it much easier to smoothly transition control. It may not sound like much time, but consider that in a self-driving car, the latency required to avoid a collision could be in the range of milliseconds. By the time the driver realises (s)he has to take control, it's too late.
In planes, when the autopilot disconnects because of some problem there's usually plenty of warning (including a sound like https://www.youtube.com/watch?v=8XxEFFX586k ) and the pilot(s) have some time, seconds or more, to assess the situation and take control. Despite how fast planes fly, the rules of separation and general vastness of airspace make it much easier to smoothly transition control. It may not sound like much time, but consider that in a self-driving car, the latency required to avoid a collision could be in the range of milliseconds. By the time the driver realises (s)he has to take control, it's too late.