As far as Meth (SPEED). A lot depends on the dose and usage. In some cases it can speed up reaction times, and help as a cognitive enhancer.
But, using it to prevent drowsiness may have other impacts including perhaps attention deficits.
I wonder if the impact could be similar to making poor choices with sleep deprivation, even if one is moderately alert.
I'm not sure if one can say SPEED was the only cause of the accident, but it may have been one of several factors that increased the risk.