From what i read about uber, i can assume it is pretty safe

No cash, route mark by gps, passenger need to key in their details(CC) any assault you can asked uber about their details no?

Maybe if you really go for it, you can equip yourself with pepper spray, better make it visible to the passeger so they know you are not an easy target, and those personal alarm key chain, high decible one....

And maybe you can request the passanger not to sit directly behind you, so you can observe your passenger behaviour...