That's the problem with statistics. Most of the time, people who are smoking pot are also doing other drugs, including alcohol. That's why the statistics here are almost completely meaningless. Except the obvious one - no person EVER has died of an overdose of marijuana.
The fact of the matter is that marijuana is significantly less dangerous a drug than alcohol or cigarettes - and the fact that it is illegal while the others are not is due not to facts about the drug, but other political maneuvering.
It's also necessary to consider that marijuana-related illnesses and incidents (such as traffic accidents) are usually just lumped into the stats for other substances. The stats for the health effects of tobacco, for example, are derived from statistics on a variety of health problems linked to tobacco, whether the sufferer actually smoked or not. This means that if long-term marijuana smoking DID cause lung cancer and emphysemia, we'd never know because it would just be labeled a "smoking-related death" and left at that.
Likewise, people DO get in traffic accidents under the influence of marijuana for the same reasons they do with alcohol: both of them screw with your reaction time and judgement ability. But a DUI is a DUI, and they all get counted together, not separated out by WHAT you were "under the influence" of.
Another thing to consider is that marijuana use, being illegal, isn't anything like as widespread as either alcohol and tobacco, so OF COURSE it doesn't have comparable statistics.