Amphetamines are detectable in urine for around one to three days after use. Methamphetamines stay in the system slightly longer, for around three to five days. Amphetamine use will show in hair tests for about 90 days. I'm afraid I have no information on the length of time saliva tests will show positive.

The issue of driving isn't just about the immediate effects: obviously your driving skills will be affected while it is in your system, which also depends on what you take and what else you have in your system at the same time (alcohol, XTC, pot etc). Amphetamines in small amounts sharpen reflexes and improve concentration for a while after you take them. But they also impair judgement, make you feel bullet-proof and lead to risky behaviour.

As they wear off, attention, concentration, energy levels and performance behind the wheel all drop below par. You really should stay away from driving and using machinery for as long after you use. Smoke on and off for three days and you should not drive for those three days or for the next three.