You want to go to a bar that requires a drive, but a good cab is hard to come by in Pittsburgh. Why not rent a limo?
These guys show up on time, and are friendly no matter what state your friends are in. $5 per person in the city, anytime, with a minimum of $20 per ride. $7 if you want to go to the suburbs. The limos are clean.
Just be sure to schedule well in advance. You'll need to be flexible about pick up and drop off times, as the demand outstrips their available drivers.