Changing directions on the fly, modifying driving path...

Hopefully I'm going to ask this right, ha, but I'm curious if there's a way to avoid back roads and only use highways \ or the main drag. Or another way to ask; is if you want to use the turnpike instead of 95, instead of missing the former until it points you to the latter, which isn't always guaranteed to begin with, can you change directions on the fly? (Again without having to miss what Maps is suggesting) Thank you!