That's how my mind works too. And,, it can be pretty useful. Or not. Kind of like @joeylittle suggested, you can modify it.Plan B, C, D. Or really it's 'in case my car dies, how will I get there' Plan A, B, C etc. Its how my mind works,
I work really hard at only running scenarios for problems that actually exist. If I get going on all the problems that MIGHT exist, it gets overwhelming and I end up nearly immobilized. It's sometimes just to much.
In this case, the way I'd look at the transportation issue is, "it might be a long ways from the train the office. Worth noting. If it turns out to be true, that's something I'll have to deal with." But I'm not going to spend the energy dealing with it until I know what the situation really. While assessing the situation, "how am I going to get there?" is definitely something I'm going to pay attention to, but there's no sense solving the problem until you know what is. You can end up 'solving' a lot of imaginary problems. Or being so overwhelmed things get much harder than they have to be.