I'll give you a great example: I used to work in Rockafeller Center (the former Exxon Building, now just called 1251 6th). There's a subway station in the building. It goes, express, on several lines, to W 4th street (actually 2 Cornelia, corner of W 4th and 6th), where I lived. Couldn't be easier, right? But, amazingly enough, grabbing a yellow above ground gets you uptown way faster than MTA unless it's extreme rush hour or raining.
If they can't compete on a straight line with express service, how can they hope to compete for ad-hoc trips that don't follow straight lines?
You're at 1st Avenue and 47th; you want to go to West Broadway and Spring.
Good luck.
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The NYC subway is great; don't get me wrong. But the frothing you hear about it is unwarranted.
/jordan