Bus stops are my favorite places to approach. The girl is stationary (not moving), she's usually bored waiting for the bus, and unless she's a total ice queen, you can have an awesome conversation in no time.
I did this approach last week actually.
"did the 95 pass by?"
"no/yes"
"ah thanks, my name is <> by the way"
"im <>"
"nice to meet you, (sometimes I'll say "that's a pretty cute name" if it's a unique one, I didn't do it last week tho), where are you coming from?"
"work/hair salon/feminist rally/etc"
ask more about that, get her talking about her life, etc, make her comfortable, make her laugh at least once, if she asks you anything, be mildly c&f, then once your or her bus comes, tell her you wanna get to know her better over coffee, and ask for her to punch her number into your phone.