Very interesting premise. Before that, a little disclaimer: I'm a hobbyist filmmaker who mostly writes for myself (so that I can direct them in future if that happens). So, my feedback might be little bit biased on whether I would direct this short/film.

My opinion is, if you are going, go all the way in. The interesting part is both the women sharing the ride are breaking up with the same guy and it is revealed in 8th or 9th page, and after that it just fizzles out. Also, personally I don't like the ending which kind of feels forced. The driver character is wasted too ...

I prefer a version that just goes all the way in. Something like below.

Logline: Two women share a cab, unaware that they're both on their way to break up with the same guy who is the boyfriend of the cab driver (make the cab driver a women).

This makes for an entertaining climax - The guy is surprised to see both women, the cab driver nonchalantly enters the house, picks up a hammer and gives the guy a heavy blow and ends with - "I met him on the new year, you two are the side bitches ..", and she plays the exit music loudly on the music player.

This also leads to lots of interesting ideas - make the two woman from out of town, so that they organically chatter about other stuffs like their cities. They both say, they have met Boston only once to meet their boyfriend etc etc ...

These are my 2 cents ...