How can I ask a girl out, I see every day on a train?

[Adam B]

Okay, so this has probably been covered a gazillion times before. It's the one possible situation that has millions of different methods and it's own ettiquette to deal with, but I'd like to figure out the best way for me.

I live in the UK and I commute each day to work. However, I get off only one stop down the line to the main town and there's this stunning girl I see almost every week-day on the same train. She's always alone. She even get's off on the same stop as me and every now and again I find myself walking either beside her, in front or behind on our way to our respective jobs. So far I've said nothing, nada, zip, zilch, zero. Sweet F.A.
She flashed a smile to me once as I let her pass to get out of the train car. For all I know, I don't even register to her.
A sad state, considering I'm a sociable sort and not bad looking either. But when it comes to the truely stunning women that make me trip myself up, I get intimidated very easily and let those opertunites pass by.