Let me look into my crystal ball about driverless cars...

Driverless cars are years away from existing in the real world, yet some pointy-heads at the University of Michigan in Ann Arbor have decided that they will cause more pollution. 

How?

A self-driving car would make more trips to finish the same tasks, the University of Michigan researchers said. It might drop off one parent at work, return home to pick up the other, and then take the kids to school, return home, then start the return cycle.

This is taken from a Bloomberg article about the research. Without a link to the original research, who knows what conclusions the researchers actually came to or their rationale but from the Bloomberg article, it seems a lot like crystal ball gazing.