What does「電車に乗ってたらなんだっていうんだろね」mean in this context?

Question

For context, in the light novel Hige wo Soru, Soshite Joshikousei wo Hirou's chapter 12:

the main character Yoshida leaves for work and his friend Sayu is left alone at their apartment. He's thought before that she must be bored at home all day while he's gone. This chapter is from her perspective, and she explains the she feels lonely now that he's left and later she starts idly thinking to herself about Yoshida while she does dishes, thinking that Yoshida is probably at the station and should've boarded the train by now. Then there're these lines:

そんなことを考｛かんが｝えて、すぐに可笑｛おか｝しくなった。

「電車｛でんしゃ｝に乗｛の｝ってたらなんだっていうんだろね」

どれだけ独｛ひと｝り言｛ごと｝を言｛い｝っても、聞｛き｝いている人｛ひと｝はいないし、返事｛へんじ｝をする人｛ひと｝はいない。

The first and third lines make sense to me.

But the second one's really confusing. I don't understand how the ってたら, the なんだって, and the いうんだろね all connect. Can someone help me please?

For further context, after these lines she starts thinking about how she talks to herself a lot when Yoshida's gone.

Answer 1

Ignore my suggestion in the comments! Actually I think the way you should interpret this is "what difference does it make if he's riding the train?" Grammatically some key points are:

乗ってたら is a contraction is 乗っていたら, which is a condition of 乗っている ("is riding")

なんだっていうんだ is kind of a set expression for "what difference does it make?" それがどうした is another expression with the same meaning. You could also translate it as "so what?", "who cares?", and so on.