Marijuana, even in low to moderate doses, negatively affects driving performance in real situations. While previous research on alcohol effects alone show that alcohol at BACs around .10 is far more impairing than low or moderate THC doses alone, marijuana does impair driving performance. Drivers would be less than normally able to avoid collisions if confronted with the sudden need for evasive action. The effect of combining moderate doses of alcohol and moderate doses of marijuana resulted in a dramatic performance decrement and levels of impairment, as great as observed when at 0.14 BAC alone.