A growing body of research indicates that marijuana is on balance less of a road hazard than alcohol. Various surveys have found that half or more of fatal drivers have alcohol in their blood, as opposed to 7 - 20% with THC, the major psychoactive component of marijuana (a condition usually indicative of having smoked within the past 2-4 hours).(3) The same studies show that some 70 - 90% of those who are THC-positive also have alcohol in their blood. It therefore appears that marijuana by itself is a minor road safety hazard, though the combination of pot and alcohol is not. Some research has even suggested that low doses of marijuana may sometimes improve driving performance, though this is probably not true in most cases.(4) Two major new studies by the National Highway Transportation Safety Administration have confirmed marijuana's relative safety compared to alcohol. The first, the most comprehensive drug accident study to date, surveyed blood samples from 1882 drivers killed in car, truck and motorchycle accidents in seven states during 1990-91.(5) Alcohol was found in 51.5% of specimens, as against 17.8% for all other drugs combined. Marijuana, the second most common drug, appeared in just 6.7%. Two-thirds of the marijuana-using drivers also had alcohol. The report concluded that alcohol was by far the dominant drug-related problem in accidents. It went on to analyze the responsibility of drivers for the accidents they were involved in. It found that drivers who used alcohol were especially culpable in fatal accidents, and even more so when they combined it with marijuana or other drugs. However, those who used marijuana alone appeared to be if anything less culpable than non-drug users (though the data were insufficient to be statistically conclusive). The report concluded, "There was no indication that marijuana by itself was a cause of fatal accidents." (It must be emphasized that this is not the case when marijuana is combined with alcohol or other drugs). The second NHTSA study, Marijuana and Actual Driving Performance, concluded that the adverse effects of cannabis on driving appear "relatively small" and are less than those of drunken driving. (6) The study, conducted in the Netherlands, examined the performance of drivers in actual freeway and urban driving situations at various doses of marijuana. It found that marijuana produces a moderate, dose-related decrement in road tracking ability, but is "not profoundly impairing" and "in no way unusual compared to many medicinal drugs." It found that marijuana's effects at the higher doses preferred by smokers never exceed those of alcohol at blood concentrations of .08%, the minimum level for legal intoxication in stricter states such as California. The study found that unlike alcohol, which encourages risky driving, marijuana appears to produce greater caution, apparently because users are more aware of their state and able to compensate for it (similar results have been reported by other researchers as well.(7)) It should be noted that these results may not apply to non-driving related situations, where forgetfulness or inattention can be more important than speed (this might explain the discrepancy in the Baltimore hospital study, which looked at accidents of all kinds). The NHTSA study also warned that marijuana could also be quite dangerous in emergency situations that put high demands on driving skills.