If you ask, "Hey, how's your day going?" and they respond with a one-word answer, they probably don't want to talk. But if they start telling a crazy story about the last passenger... BOOM, fun English practice!
Other questions that will almost always elicit a good answer:
"How do you like driving for Uber?"
"What's better, Lyft or Uber?" (many drivers drive for both, and they usually have an opinion!)
"What's the craziest thing that's ever happened for you while driving for Uber?"
"It's my first time here—what's your favorite part of this city?"