southbound is a confusing word, when you dont know its meaning, despite the fact that part of the word is recognizable. If a person does not know what the whole word means, disecting it might not help. I remember when I first time encountered it it was the name of the song and I had to look it up. Even though I suspected that it meant direction of some sort. And I wasnt preoccupied with some afterTO routine.
Every new word even among other familiar onces might throw you off because you realize that i might mean something completely opposite to what you think it would mean.