As many can testify, i'm well know to be one who hit almost everything on city maps/tracks: poles, road signs, hydrants and so on
so that's the reason because i don't like too much urban tracks (where usally i'm not so fast for that reason).
But anyway, i can agree with
TorQueHQ and
Khrono Fujiwara:
1) do you a favor and disable (remove from trunk) the racing lines, they can be useful just the first time on the track, but then they teach you nothing useful. If you want to go fast, you need to pratice and find the fastest lines for your driving style and your car. Also during a race with ghost off, you have to improvise because you can find another car on the best line, or you need to use another line to try an overtake etc, so you need to find the better line for the situation, something you can't learn from the game racing lines
2) with pratice, you're not only improving your lines, how to adapt etc, you start to know every corner of every map/track, so you can remember where a dangerous object is and how go fast in that point without hitting anything, another thing that the game racing lines didn't teach to you.