How would this reduce or increase traffic? The demand is staying the same.
Presumably the increased supply of "drivers" going to SFO will lower rideshare prices for everyone and make public transit less appealing
Public transit connections to SFO are shit-tier. Rideshare prices have little to do with it.
You can BART from there to downtown, that beats a lot of cities. (yes, yes, BART quality can vary, but still.)
What about the rest of the Bay?
I've taken BART and it's fine but expensive (there's an airport fee that's something like $8 per ticket each way). For groups/families I could see rideshare winning on both cost and convenience.
Waymo can deliver as many rides as Uber with a small fraction of the number of vehicles.