Yes, or relativistic velocities. I figured that harm due to the energy of the collision is limited by death, while time spent on road tends to zero, but your mention of shockwaves brings to mind that a sufficiently high-energy collision would also be a danger to otherwise uninvolved road users, or residents of nearby towns, so my first assumption was incorrect. (I leave aside the problem of maintaining control of a mach 3 road vehicle as an implementation detail.)