I think you are spot on with regards to the 'unavoidable artefact' statement. That said if the road is straight there is no reason why the tokens couldn't be moved D3 spaces backward at the end of each turn
My interpretation of the rules is that the movement of the miniatures represents their relative speed to each other, as a result, on braking, you move backwards (because everybody else is for a moment moving forward faster than you). However, this clashes with the fact that objectives, such as items to be picked up, are fixed on the board, so if you are braking, you actually move away from them, same with obstacles etc. Is this just an unavoidable artifact of the relative movement system or am I misinterpreting something?