Soon after voters in Washington state passed Initiative 502 in November 2012, legalizing private recreational marijuana use by adults, smokers gathered at the Space Needle in Seattle to celebrate. Law enforcement officers indulged them, overlooking for an evening the fact that the law does not allow public consumption.
Now the party's over, and legislators and others in Washington and Colorado, which passed a similar measure, are grappling with a number of legalization issues, including how to handle people who use marijuana and then drive.
If you live in Colorado or Washington, or plan to travel there, here's an update on how the new marijuana laws affect driving now and how the impact of legalized pot may play out.
Decisions that officials make in Colorado and Washington are likely being watched in many other states that are debating whether to legalize the use of non-medical marijuana.
Two States, Two Different Laws
Washington and Colorado handled the legalization differently when it comes to marijuana use by drivers.
Washington state has defined a standard for how much of marijuana's active ingredient, tetrahydrocannabinol or THC, must be in the bloodstream before a driver can be charged with driving under the influence (DUI).
Under the new law, it is not lawful to operate a motor vehicle with a level of 5 nanograms per milliliter of THC in the blood, as detected by a blood draw.
If a driver has a level of 5 nanograms THC or greater, he or she will face the same conviction as a driver under the influence of alcohol or other drugs.
For a first offense, punishment includes suspension of the license for 90 days (even before conviction) and fines, which vary by court, says Brad Benfield, a spokesman for the Washington Department of Licensing.
If a driver is convicted, that license suspension could extend to up to four years. Conditions to get it back vary, possibly including drug rehab classes, court fines and licensing reissue fees.
"It does set a legal standard of intoxication [with marijuana] where one didn't exist before," Benfield says of the new law.
Colorado's Amendment 64, also passed in November 2012, legalizes private pot use by most adults and allows them to grow a small number of marijuana plants. However, no legal blood limit was set for drivers. The debate about what should be done is ongoing.
In one of the latest drafts in Colorado, legislators are recommending that drivers who test over the legal THC limit could argue they were not impaired.
The same provision does not exist in state law that's applied to those charged with being under the influence of alcohol. If they have a blood alcohol level of .08 or higher, they are automatically considered impaired.
"The ability to drive does not play in'' when a driver is suspected of driving under the influence of alcohol, says Jared Adams, a Denver attorney.
The new proposal, which requires an evaluation based not just on blood levels but impairment linked with marijuana, will be introduced in the 2013 legislative session, Adams and others predict.
Comparing Alcohol and Marijuana
The effects of alcohol can't be compared, apples to apples, with the effects of marijuana, says Lenny Frieling, an attorney and chairman of the Colorado chapter of the National Organization for the Reform of Marijuana Laws (NORML).
"Unlike alcohol, the correlation between active THC in your blood and impairment in driving is poorly correlated," he says.
Paul Armentano, deputy director of NORML nationally, agrees. "There is much greater variability about how marijuana influences behavior [compared to alcohol]," he says. The same amount of marijuana, for instance, may greatly affect a new smoker but not an experienced or chronic smoker, Armentano says.
Body weight can play a role, too, in one's reaction, he says.
Maximum blood levels of THC occur before the onset of impairment, he says. "As the levels go down, impairment goes up."
"The body processes marijuana in a fundamentally different manner than it does alcohol," Armentano says. For that reason, blood tests for marijuana are not impairment tests, he says, but simply detection tests that don't reflect the degree of impairment.
More study is needed, he says, to figure out how to gauge if someone's driving is affected by his marijuana use. It's a matter of identifying the best tests to detect actual impairment from marijuana use, he says.
While the effect of marijuana are variable, he says, "generally users perform most poorly 20 to 40 minutes after inhalation, but after 60 minutes their performance often begins to return to what it was before smoking."
Having a medical marijuana prescription has no impact on whether a driver will get a DUI, Frieling says, although many motorists think otherwise. If they are under the influence, they will likely be charged, he says.
Research on Alcohol, Marijuana and Driving
Marijuana and alcohol do affect drivers differently, as Armentano says and several medical studies suggest.
In one study, published in 2009, Yale researchers looked at the effects of marijuana and alcohol on the ability to drive, reviewing published studies.
Both substances impaired driving skills, they found. However, they found that the effects of marijuana varied more greatly among people than did alcohol effects.
They also found that marijuana smokers tend to compensate while driving by a variety of strategies, such as driving more slowly or passing less often.
However, combining alcohol with marijuana eliminates the ability to use the strategies, they found.
In a more recent study, published in 2012 in the journal Clinical Chemistry, researchers who reviewed published evidence found that blood THC concentrations of 2-5 nanograms per milliliter ''are associated with substantial driving impairment, particularly in occasional smokers."
They found that higher blood THC concentration is linked with increased crash risk, although other experts disagree. But studies don't show a direct correlation between impaired driving and THC concentration, the researchers say.
Combining alcohol and marijuana definitely increases the risk of crashes, experts say.
Advice for Drivers
Whether you are trying to avoid drivers who are under the influence of marijuana or trying to avoid your own legal problems, knowing a ''safe'' interval between smoking and driving is wise.
However, there's no agreement on what that interval is.
The National Highway Traffic Safety Administration, on its Web site, states: "Marijuana has been shown to impair performance on driving simulator tasks and on open and closed driving courses for up to approximately 3 hours."
Among the impairments are worse car handling, increased reaction times, impaired estimates of distance, sleepiness, lack of coordination and less vigilance, NHTSA says.
Other expert sources say that 3 hours is not nearly enough time to wait before driving.
Steve Graham, an attorney in Spokane and a former prosecutor, has counseled medical marijuana users.
"After smoking they need to wait until they are clear-headed enough," he says. "My advice would be [to wait] for 10 hours, particularly for frequent users. If in doubt, you really need to stay off the road."
Advice about a ''safe'' time interval also hinges, experts say, on whether the person is a new user or a veteran. Novices will likely be affected more strongly. The potency of the marijuana also affects its impact.
Frieling, the Colorado attorney and state NORML chairman, says the 3 hours suggested by NHTSA seems conservative.
"I tell [users] an absolute minimum of 3 hours, and that that isn't a safe number but it may be a practical number. A small number of people will have a THC level of 5 and over after [that window]."
It's hard to advise a set time, says Adams, the Denver attorney. The best advice, in his opinion: Get a good night's sleep before driving again, "and be very careful."