At Green Cab, Athan the manager, has on the Green website "expect the unexpected" [Heraclitus (c.535 BC - 475 BC]. You don't have to be a rocket scientist to know the holidays especially can be dangerous.
Athan today copied Green Cab relaying an SFPD bulletin that there had been a robbery on a Yellow driver Dec 1 the other day. Would have been nice had they stated the time of the pick up and robbery. And on Jan 11 it will have been one year since driver Singh was stabbed on States Street. Nothing has been done.
The way it is now your safety is largely a crap-shoot depending on your company and dispatch service. To some extent it involves big company v. little company. But really it's a worker protection issue and it shouldn't be a crap shoot. The SFMTA exists in part to provide uniform regulations including driver safety.