Field Sobriety test for drivers smoking pot

I have heard that a problem with marijuana is that you can't test for whether or not a driver is under the influence while driving.

Why not just use the same field sobriety test that they use for suspected DUIs? Just have someone walk the straight line, touch their nose, alphabet backwards, etc.

If that shows the cop that a suspected DUI is capable of driving, why would you need something else for someone suspected of driving while high?


Field Sobriety test for drivers smoking pot