MatthewHSE - 8:21 pm on Oct 11, 2010 (gmt 0)
The sheer volume of ground-based traffic is vastly higher than what an airplane has to deal with, plus that volume is crowded into a much smaller area - namely, roads. ;)
Driving a car vs. flying an airplane- which is more difficult?
Plus, I suspect that variables in the road itself are far more complicated to a computer than the z axis could be.