[Zeke]

Real rumble strips ought to do the job. They seem to rattle the car enough to lose some time but in themselves don't do great harm. Too tall a berm and you start ripping off parts that other cars can hit potentially causing enough damage to cause a crash. Also tall berms can launch a car.

A wonder if a study has ever been done on the spacing of such strips. It may only take 2 per turn to upset the car. It's all in some kind of harmonics.