Using linepick and setting specific things to happen when the car reaches an incline or whatever is more of a hack job than car physics.
perhaps, but there is still a physics system behind it that controls the movement of the car when on the ground - my current system allows for controllable power-oversteer and full-on drifting, but also allows for variations in the car such as front and rear-wheel drive, mass, inertia etc.. I've now got it checking the ground polys also so that mud/gravel is more slippery than tarmac.