Drugged Driving Has No Definition, but It's Definitely Illegal

Is Driving High on Marijuana Safer Than Driving Drunk? [ or driving sober?!! ]
For decades, marijuana advocates have argued that pot has a significantly different effect on driving ability than alcohol. But if you take the word of one auto insurance company, stoned is actually the safest way to drive. 4AutoinsuranceQuote.org is making that case based on years’ worth of scientific studies, including some from the US National Highway Transportation Safety Administration that found motorists under the influence of marijuana tended to drive slower and have accident responsibility rates lower than those of drug-free drivers.
http://blogs.lawyers.com/2012/04/cruising-the-high-way-safer-than-drunk-driving/

A 2002 review of seven separate crash culpability studies involving 7,934 drivers reported, “Crash culpability studies [which attempt to correlate the responsibility of a driver for an accident to his or her consumption of a drug and the level of drug compound in his or her system] have failed to demonstrate that drivers with cannabinoids in the blood are significantly more likely than drug-free drivers to be culpable in road crashes.” [Chesher et al. Cannabis and alcohol in motor vehicle accidents. In: Grotenhermen and Russo (Eds) Cannabis and Cannabinoids: Pharmacology, Toxicology, and Therapeutic Potential. New York: Haworth Press. 2002: 313-323.]

But, unlike with alcohol, the accident risk caused by cannabis, particularly among those who are not acutely intoxicated, appears limited because subjects under its influence are generally aware of their impairment and compensate to some extent, such as by slowing down and by focusing their attention when they know a response will be required. [Allison Smiley. Marijuana: On-Road and Driving Simulator Studies]

This response is the opposite of that exhibited by drivers under the influence of alcohol, who tend to drive in a more risky manner proportional to their intoxication.[United Kingdom's Advisory Council on the Misuse of Drugs.  The Classification of Cannabis Under the Misuse of Drugs Act of 1971. 2002: See specifically: Chapter 4, Section 4.3.5: "Cannabis differs from alcohol; ... it seems not to increase risk-taking behavior. This may explain why it appears to play a smaller role than alcohol in road traffic accidents."]
 

Cannabis use is associated with only marginal increases in traffic accident risk, comparable to anti-histamines and penicillin.

An investigator from Aalborg University and the Institute of Transport Economics in Oslo assessed the risk of road accident associated with drivers’ use of licit and illicit drugs, including amphetamines, analgesics, anti-asthmatics, anti-depressives, anti-histamines, benzodiazepines, cannabis, cocaine, opiates, penicillin and zopiclone (a sleeping pill).  His study reviewed data from 66 separate studies evaluating the use of illicit or prescribed drugs on accident risk; the study found that cannabis was associated with minor, but not significantly increased odds of traffic injury (1.06) or fatal accident (1.25). By comparison, opiates (1.44), benzodiazepine tranquillizers (2.30), anti-depressants (1.32), cocaine (2.96), amphetamines (4.46), and the sleeping aid zopiclone (2.60) were all associated with a greater risk of fatal accident than cannabis. Anti-histamines (1.12) and penicillin (1.12) were associated with comparable odds to cannabis. 

Studies have shown marijuana users are Safer Drivers than either drunk drivers, or sober ones.
http://blogs.lawyers.com/2012/04/cruising-the-high-way-safer-than-drunk-driving/

One study, entitled "Medical Marijuana Laws, Traffic Fatalities, and Alcohol Consumption" conducted in November 2011 provides evidence that marijuana is a safer substitute for alcohol when it comes to health and also makes for safer drivers.

Top Ten Reasons Marijuana Users Are Safe Drivers

When you combine all of the main results of these two decades worth of scientific research studies, the following 10 reasons marijuana drivers are safer than drunk drivers comes out like this:

1. Drivers who had been using marijuana were found to drive slower, according to a 1983 study done by U.S. National Highway Transportation Safety Administration (NHTSA). This was seen as a factor in their favor, since drivers who drank alcohol usually drove faster and that is part of the reason they had accidents.

2. Marijuana users were able to drive straight and not have any trouble staying in their own lanes when driving on the highway, according to a NHTSA done in 1993 in the Netherlands. The study determined also that the use of marijuana had very little effect on the person’s overall driving ability.

3. Drivers who had smoked marijuana were shown to be less likely to try to pass other cars and to drive at a consistent speed, according to a University of Adelaide study done in Australia. The study showed no danger unless the drivers had also been drinking alcohol.

4. Drivers high on marijuana were also shown to be less likely to drive in a reckless fashion, according to a study done in 2000 in the UK by the UK Transport Research Lab. The study was done using drivers on driving simulators over a period of a month and was actually undertaken to show that pot was a cause for impairment, but instead it showed the opposite and confirmed that these drivers were actually much safer than some of the other drivers on the road.

5. States that allow the legal use of marijuana for medical reasons are noticing less traffic fatalities; for instance, in Colorado and Montana there has been a nine percent drop in traffic fatalities and a five percent drop in beer sales. The conclusion was that using marijuana actually has helped save lives. Medical marijuana is allowed in 16 states in the U.S.

6. Low doses of marijuana in a person’s system was found by tests in Canada in 2002 to have little effect on a person’s ability to drive a car, and that these drivers were in much fewer car crashes than alcohol drinkers.

7. Most marijuana smokers have fewer crashes because they don’t even drive in the first place and just stay home thus concluded more than one of these tests on pot smoking and driving.

8. Marijuana smokers are thought to be more sober drivers. Traffic information from 13 states where medical marijuana is legal showed that these drivers were actually safer and more careful than many other drivers on the road. These studies were confirmed by the University of Colorado and the Montana State University when they compared a relationship between legal marijuana use and deaths in traffic accidents in those states. The studies done by a group called the Truth About Cars showed that traffic deaths fell nine percent in states with legal use of medical marijuana.

9. Multiple studies showed that marijuana smokers were less likely to be risk takers than those that use alcohol. The studies showed that the marijuana calmed them down and made them actually pay more attention to their abilities. All of these tests and research studies showed that while some people think that marijuana is a major cause of traffic problems, in reality it may make the users even safer when they get behind the wheel.

10. Marijuana smoking drivers were shown to drive at prescribed following distances, which made them less likely to cause or have crashes.

.. stick *that* in your pipe, and smoke it!

http://www.theweeklyconstitutional.com/news/headlines/1035-why-you-should-always-spark-up-before-hitting-the-road