I think expecting a backup driver to pay that kind of attention on a continuous basis is unrealistic on Uber's part.

Are you familiar with Threat Image Projection? It's a system where baggage scanning machines put in images of fake threats into real baggage. Why is this necessary? It's because regular baggage doesn't have enough in the way of actual threats to keep operators alert.

I think it's the same deal with being a backup driver for a robot car. Sure, they should be ready to take over when the car asks for help, and it's great if they notice a problem and stop the car. But I don't think expecting them to have this kind of reaction time is realistic.

(That may not stop Uber from throwing the backup driver under the bus, though.)