Pubdate: Sun, 15 Apr 2012
Source: St. Louis Post-Dispatch (MO)
Copyright: 2012 St. Louis Post-Dispatch
Contact: http://drugsense.org/url/qFJNhZNm
Website: http://www.stltoday.com/
Details: http://www.mapinc.org/media/418
Author: Maggie Clark

LEGAL POT RAISES CONCERN OVER 'DRUGGED DRIVING'

Lawmakers Want Limits, but Impairment Is Difficult to Measure.

WASHINGTON  Twelve years after Colorado legalized the use of 
marijuana for medicinal purposes, more than 85,000 people have been 
certified by the state health department to use it. Now, there is 
increasing concern about a rise in traffic accidents caused by people 
under the influence of marijuana.

Between 2006 and 2010, more than 300 fatal accidents involved drivers 
who tested positive for cannabis, according to the Colorado 
Department of Highway Safety. That's why Republican state Sen. Steve 
King wants Colorado to set a legal limit for marijuana intoxication, 
somewhat similar to the 0.08 percent blood-alcohol limit states put 
on driving. And in California, Democratic Assemblywoman Norma Torres 
wants to set a zero-tolerance ban on driving under the influence of 
any drug, including marijuana.

But bills put forward by both King and Torres have run into 
opposition from those who say the science around what marijuana does 
to the body and mind is not conclusive enough to set a legal limit. 
In Colorado, critics also note that King's approach would cost the 
state public defender's office about $600,000 per year to defend 
those accused of "drugged driving" charges.

Yet concerns over cannabis intoxication won't go away. Voters in 
Colorado and Washington state will decide whether to legalize 
recreational marijuana use, while a dozen more states are considering 
legalizing marijuana for medical purposes.

How does marijuana affect the body?

The active ingredient in marijuana is called 
delta-9-tetrahydrocannabinol, or THC. Whether marijuana is ingested 
through smoking or eating, THC rapidly goes through the bloodstream 
to the brain. In the brain, THC slows down receptors that communicate 
brain functions between synapses, throwing the brain's natural 
information flow off balance. Users experience diminished pain 
sensitivity, which explains marijuana's medicinal purpose. But users 
also experience slowed reaction time, impaired memory function, 
impaired coordination and altered judgment.

How does marijuana's effect on drivers compare to alcohol?

Although the symptoms for THC intoxication are similar to alcohol 
intoxication, the effects on drivers are very different. According to 
a study by researchers from Yale University, alcohol-impaired drivers 
struggle with complex tasks, such as merging onto a crowded highway, 
but can generally perform more automatic functions such as turning on 
the car. Marijuana users, however, can better handle complex 
situations than simple tasks like following the curve of a road. The 
Yale study also notes that the effects of cannabis can vary a lot 
more between individuals than with alcohol. Factors such as a user's 
age, weight, tolerance and smoking technique all can make a large 
difference in how the body absorbs THC.

Users of alcohol and marijuana also differ in their perceptions of 
their own impairment. Alcohol users tend to underestimate their level 
of impairment and drive faster and more recklessly. Drivers with a 
blood-alcohol level of 0.04 percent - half the legal limit in most 
states - experienced impaired driving performance even though the 
drivers considered themselves as unimpaired, according to a 
frequently cited 1993 study from the National Highway Transportation 
Safety Administration.

By contrast, marijuana users tend to overestimate their impairment 
and don't display as many obvious impairment symptoms. In the same 
government study, drivers who were given about one-third of a joint 
to smoke rated themselves as impaired even though their driving 
performance was not.

How long does it take for marijuana's effects to wear off?

Marijuana's impairment effects usually wear off within about three 
hours from the time of smoking or eating it. But traces of THC stay 
in a user's body for up to a month. This can make testing for 
intoxication problematic because THC shows up in blood tests long 
after the symptoms that impair driving have gone away.

How big of a problem is marijuana-impaired driving?

No one is quite sure. One measure comes from a voluntary national 
roadside survey conducted by NHTSA in 2007. About 14 percent of 
drivers pulled over at night tested positive for the presence of 
impairing drugs in their system; the daytime figure was 11 percent. 
The study looked beyond marijuana and included both legal and illegal 
substances such as prescription drugs, stimulants and narcotics. Of 
this group, the most commonly detected drug was marijuana.

In a more recent California roadside study, conducted at night over a 
weekend, more people tested positive for THC (8.4 percent) than for 
alcohol (7.6 percent). Because of the long time THC can remain in the 
body, however, the study was not a clear measure of impaired driving.

How does the risk of traffic accidents following marijuana 
consumption compare with the risks of accidents after alcohol consumption?

Driving within three hours of consuming cannabis increases the risk 
of vehicle crashes by about two or three times, according to research 
published this February from Mark Asbridge, an associate professor at 
Dalhousie University in Canada. Concerning as that is, it is much 
less of a risk than alcohol consumption, which increases vehicle 
crash risk by five to 16 times.
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MAP posted-by: Jay Bergstrom