Lyric discussion by razehate 

Cover art for Highway lyrics by Ingrid Michaelson

i actually thinks that it's about the whole empty nest syndrome,

like in the first line it mentions 17 years most kids are 17 or 18 when they graduate high school and go off to college

so she's letting him go driving him to his school somewhere along the east coast

and then she relives the steps of his life from his birth to the current drive in the last stanza i picture her driving away from the college tearing up and thinking about how he's not her baby anymore