Welcome to PGD!

Your game sure looks mighty nice! Im curious how did you do the background. Are those large imagemaps?

Anyhow, your question:
Changing de pixels of the surface like you suggested is certainly an option, but a very slow one a that, so not very favourable. Alternative you could draw a line between the point where braking starts and where it ends.
Drawback of this approach is that you can't create curves very easily.