"Every state needs a law ... defining, in essence, a crime divorced from impairment; ... that says if you use an illicit drug and drive,

you have broken the law. ... We need to treat DUID as important [an offense] as murder, rape, and child molestation."

-- John Bobo, Director, National Traffic Law Center. "Enforcement and Prosecution of Drugged Driving Laws," speech given February 23, 2004

"Current research does not enable one to predict with confidence whether a driver testing positive for a drug,

even at some measured level of concentration, was actually impaired by that drug at the time of crash."

-- US Department of Transportation. State of Knowledge of Drug-Impaired Driving: FINAL REPORT, September 2003

"The American public does not yet realize that driving under the influence of drugs is a problem at least as big as drunken driving. 

There are two appropriate action steps: Routine roadside tests for recent drug use [and] the universal application to all drivers of the per se standard currently applied to the nation's 12 million commercial drivers."

-- Robert L. Dupont. "Drugs and driving." Letter to the editor: USA Today. October 28, 2004

"Drug tests detect drug use but not impairment. A positive test result, even when confirmed, only indicates that a particular substance is present in the test subject's body tissue. It does not indicate abuse or addiction; recency, frequency, or amount of use; or impairment."

-- US Department of Justice. Drugs, Crime, and the Justice System. December 1992

There's a new front in law enforcement's self-proclaimed "War on Drugs" and its name is DUID.

DUID, short for "driving under the influence of drugs," is the new buzzword among politicians and police -- however, in this case, words can be deceiving. Though billed by its sponsors as a necessary tool to crack down on "drugged driving" offenses,1 in reality, DUID laws -- in particular "zero tolerance" per se laws -- have virtually nothing to do with promoting public safety or identifying motorists who drive while impaired. Rather, the enactment and enforcement of zero tolerance DUID legislation is a direct and calculated assault on the lives and liberties of marijuana smokers, many of whom are just now beginning to feel the laws' effects.

DUID DEFINED

DUID laws come in various shapes and sizes, some more pernicious than others. Today, every state has DUID legislation on the books. These laws fall into three distinct categories:

EFFECT-BASED DUID LAWS

Most state DUID laws are "effect based" laws. This legislation forbids drivers to operate a motor vehicle if they are either "under the influence" of a controlled substance, or if they have been rendered "incapable of driving safely" because of their use of an illicit drug. In order for a defendant to be convicted under this statute, a prosecutor must prove that the driver's observed impairment and/or incapacity was directly associated with the ingestion of an illicit substance. To do so, prosecutors typically rely on evidence gathered by law enforcement officers at the scene of an accident (i.e., a driver's failure to pass a field sobriety test, evidence that the motorist was driving at an excessive speed, etc.), testimony from a Drug Recognition Expert (DRE), and/or a positive result from a blood or saliva test indicating recent consumption of a controlled substance. For the most part, this is a multidisciplinary standard that focuses on the totality of circumstances -- most importantly, whether the driver is observedly impaired -- and accordingly punishes motorists who drive while impaired from having recently used illicit drugs.

PER SE DUID LAWS

Per se laws prohibit drivers from operating a motor vehicle if they have greater than a set level of a drug or drug metabolite present in their system. Most of us are already familiar with the most common driving-related per se laws: those governing drunk driving which define a driver as legally impaired per se if their blood alcohol level tests above .08. Similar per se laws with strictly defined cut-off levels are uncommon for DUID legislation. (To date, only Nevada has enacted per se standards for DUID offenses.) Why? Because, according to the US Department of Transportation: "Forensic toxicologists generally have failed to agree on specific [per se levels] that could be designated as evidence of impairment. The lack of consensus about per se levels of drugs where impairment could be deemed makes it difficult to identify, prosecute or convict drugged drivers in most states."2

ZERO TOLERANCE PER SE LAWS

Predictably, politicians and police have a simple, if unscientific, solution to researchers' failure to define per se standards for DUID offenses: to enact "zero tolerance" per se laws. These laws forbid drivers from operating a motor vehicle if they have any detectable level of an illicit drug or drug metabolite present in their person's bodily fluids. In essence, zero tolerance per se laws define a new, driving-related offense that is, in the words of one of its chief proponents, "divorced from impairment." Under this standard, any driver who tests positive for any trace amount of an illicit drug or drug metabolite (an inert, non-psychoactive compound produced from chemical changes of a drug in the body), is guilty per se of the crime of "drugged driving," even if the defendant was sober. In the case of marijuana, these laws are particularly troublesome, as marijuana metabolites are fat soluble, and therefore, remain identifiable in certain bodily fluids (most notably, urine) for days and sometimes even weeks3 after past use. Consequently, under this law, a person who smoked a joint on Monday could conceivably be arrested on Friday and charged with "drugged driving," even though he or she is no longer impaired or intoxicated.

To date, eleven states (see appendix) have enacted zero tolerance per se laws: Arizona,4 Georgia,5 Illinois, Indiana, Iowa,6 Michigan,7 Minnesota,8 Pennsylvania,9 Rhode Island, Utah,10 and Wisconsin.11

FEDERAL PROPOSALS

Politicians at the federal level are also campaigning for the greater enforcement of zero tolerance per se laws. In 2004, two separate federal bills were introduced in Congress, each seeking to mandate all 50 states enact zero tolerance DUID laws.

H.R. 3907

Sponsor: Rep. John Porter (R-NV)

H.R. 3907 (see appendix), introduced in the House of Representatives on March 4, 2004, sought to withhold highway funding from any state legislature that refused to enact mandatory minimum penalties for anyone convicted of driving under the influence of illegal drugs. The bill, which failed to gain any additional co-sponsors, was referred to the following committees: House Committee on Transportation and Infrastructure, Subcommittee on Highways, Transit and Pipelines and the House Energy and Commerce Committee, Subcommittee on Commerce, Trade and Consumer Protection. H.R. 3907 failed to pass out of either committee.

H.R. 3922

Sponsors: Reps. Robert Portman (R-OH), Sander Levin (D-MI), Steven LaTourette (R-OH), Mark Souder (R-IN) and

Jim Ramstad (R-MN)

H.R. 3922 (see appendix), introduced in the House of Representatives on March 9, 2004, mandated states to enact criminal statutes sanctioning any driver who operates a motor vehicle "while any detectable amount of a controlled substance is present in the person's body, as measured in the person's blood, urine, saliva, or other bodily substance." This proposal was later added as a provision to the House transportation reauthorization bill, where it passed the House of Representatives. Although the Transportation bill eventually died in conference committee, H.R. 3922's sponsors are expected to re-introduce the bill in 2005, where it will likely enjoy majority support from House members.

BLOOD OR URINE? FLUID MATTERS

The language of zero tolerance per se laws is critical. Most zero tolerance DUID laws contain the following language: It is unlawful for any person to drive or be in actual physical control of any vehicle while there is any detectable amount of a controlled substance or its metabolite present in the person's body, as measured in the person's blood, urine, saliva, or other bodily fluid.

In order to understand the impact of this language, it is critical to comprehend the distinction between "parent drugs" and "drug metabolites." The term "parent drug" refers to the identifiable psychoactive compound of a controlled substance (e.g., for cannabis, the "parent drug" is delta-9-tetrahydrocannabinol aka THC). However, the term "drug metabolite" refers to something else all together. Drug metabolites are broadly defined as substances produced by the metabolism after a drug is ingested. Though the presence of metabolites is indicative that a certain drug may have been consumed at some previous point in time,12 they are (in general) not psychoactive,13 nor are they evidence per se that the "parent drug" is still present in the body.14 As a result, the US Department of Justice notes that a positive drug test result for the presence of a drug metabolite "does not indicate ... recency, frequency, or amount of use; or impairment."15 A recent US Department of Transportation report further adds, while a positive test for a drug metabolite is "solid proof of drug use within the last few days, it cannot be used by itself to prove behavioral impairment during a focal event."16

Recognizing the fundamental differences between "parent drugs" and "drug metabolites," let's look at the various methods of drug detection. As stated above, most zero tolerance DUID legislation allows for police to mandate a defendant to have his or her "bodily fluids" screened for the presence of drugs or drug metabolites. In most cases, the "bodily fluids" in question are: blood, saliva, and urine. However, whether or not a defendant tests positive for DUID can, in many cases, come down to a matter of which fluid is analyzed.

URINE

Urinalysis remains the most popular means of drug detection available in the United States. Courts have generally looked upon urine specimen collection as a relatively non-invasive practice, and there are national standards for urine testing in place as well as national certification programs for laboratories performing forensic urine drug testing. Nevertheless, urinalysis is not suitable for detecting drug impairment or recent drug use because the procedure only detects drug metabolites, not the parent drugs themselves. Presently, no dose-concentration relationship exists correlating drug metabolite levels to drug impairment,17 and it is well documented that the presence of a drug metabolite, even when confirmed, "does not indicate ... recency, frequency, or amount of use; or impairment."18 However, because urinalysis does offer law enforcement a multi-day window for detection (For drug metabolites other than cannabis, this window is generally two to three days;19 because marijuana's metabolites are fat soluble, their period of detection in the urine is often much longer.) and rapid response point-of-collection-testing (POCT) immunoassay devices are available on the commercial market, "a number of states with per se zero tolerance laws are currently using urine tests to enforce their laws under which the prosecutor must only show that the driver of the car had prohibited metabolites in his/her system."20 Needless to say, zero tolerance DUID laws that rely on urine testing are most likely to inappropriately target otherwise sober marijuana consumers.

BLOOD

Because blood collection is generally viewed by the courts as invasive and requires the use of medically trained personnel, its use in DUID cases is often seen as impractical. However, many European DUID laws (see appendix) rely on blood specimen collection. This is because, unlike urinalysis, both drug metabolites and parent drugs are present in the blood. In general, detection times for marijuana and other parent drugs in the blood is only a few hours,21 with levels peaking immediately after drug ingestion and then falling rapidly. As a result, the Department of Transportation notes, "In terms of attempting to link drug concentrations to behavioral impairment, blood is probably the specimen of choice."22 Nevertheless, scientists have not reached a concensus on the establishment of specific plasma concentrations that could be designated as evidence of driver impairment. However, several scientific reviews of automobile crash culpability studies have indicated that THC levels in blood serum below 5 ng/ml are not associated with an elevated accident risk.23 (Such levels may be attained within 1 to 3 hours after cannabis consumption.) Moreover, some studies suggest that "even a THC serum level of between 5 and 10 ng/ml may not be associated with an above normal accident risk."24

SALIVA/ORAL FLUID

Saliva testing is a relatively new technology. It is generally seen as non-invasive, and rapid response point-of-collection devices exist, making it (in theory) ideal for use by police on the side of the road. However, there is no consensus on appropriate cutoff levels (a designated level of metabolites that must be present in the subject's bodily fluids in order for them to test positive; this level is generally set above zero) for the confirmation of drugs in saliva, nor are there any nationally established standards for oral fluid testing.

Saliva testing detects the presence of parent drugs only, and its detection times25 are similar to blood (several hours) for drugs other than cannabis. Unlike other drugs, cannabinoids appear to be especially difficult to detect in oral fluids, as only a minute amount of the drug is excreted into the saliva.26 As a result, saliva testing appears to, at best, only detect the presence of cannabis for a period of approximately one to two hours following drug ingestion. 27

In sum, recreational marijuana consumers face their greatest risks in states with zero tolerance DUID laws reliant on urinalysis because this process detects only drug metabolites; it does not detect the presence of the parent drug itself. Sober drivers are less likely to be identified as having used cannabis in states that rely on blood and/or saliva collection because the window of detection for parent drugs in these fluids is, by comparison, relatively narrow. In cases when parent drugs are detected, there still remains no consensus regarding what concentration levels are indicative of impairment (though general estimates regarding the recency of drug ingestion may be ascertained). In cases regarding the detection of marijuana in the blood, studies have associated culpability and/or impairment at levels above 5-10 ng/ml, but not below this threshold.

HOW DANGEROUS IS "DRUGGED DRIVING" ANYWAY?

Though portrayed by politicians and police as a serious problem bordering on "epidemic," actual data is sparse concerning the prevalence of drugged driving, and more importantly, what role illicit drug use plays in traffic accidents.28 In recent years, however, researchers have begun to examine the impact of acute cannabis intoxication on driving performance and traffic safety.

While it is well established that alcohol increases accident risk, evidence of marijuana’s culpability in on-road driving accidents is much less convincing. Although marijuana intoxication has been shown to mildly impair psychomotor skills, this impairment does not appear to be severe or long lasting.29 In driving simulator tests, this impairment is typically manifested by subjects decreasing their driving speed and requiring greater time to respond to emergency situations.30

Nevertheless, this impairment does not appear to play a significant role in on-road traffic accidents. A 2002 review of seven separate crash culpability studies involving 7,934 drivers reported, “Crash culpability studies 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.”31 This result is likely because subjects under the influence of marijuana are aware of their impairment and compensate for it accordingly, such as by slowing down and by focusing their attention when they know a response will be required. This reaction 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.32

Today, a large body of research exists analyzing the impact of marijuana on psychomotor skills and actual driving performance. (Much of this research is available online through NORML’s website at: http://www.norml.org/index.cfm?Group_ID=5450.) This research consists of driving simulator studies, on-road performance studies, crash culpability studies, and summary reviews of the existing evidence. The result of this research is consistent: Marijuana has a measurable but relatively mild effect on psychomotor skills, yet it does not appear to play a significant role in vehicle crashes, particularly when compared to alcohol. As summarized by the Canadian Senate’s exhaustive 2002 report Cannabis: Our Position for a Canadian Public Policy, “Cannabis alone, particularly in low doses, has little effect on the skills involved in automobile driving.”33

To conclude, the role of cannabis consumption in on-road traffic accidents is, at worst, unknown, and at best, minimal. In either case, it is apparent that cannabis' adverse on-road impact is hardly so great as to warrant the passage and enforcement of zero tolerance DUID legislation.

SO WHO'S BEHIND THIS "ZERO TOLERANCE" CAMPAIGN?

Over the past five years, a small cabal of prohibitionists, police, drug testing proponents and toxicologists have lobbied for legislation criminalizing drivers who operate a vehicle with inert drug metabolites present in their system. That said, I'm going to name two specific individuals. The first is Michael Walsh, head of the Walsh Group,34 a federally funded organization that develops drug testing technology and lobbies for rigid workplace drug testing programs. Walsh is the former Director of the Division of Applied Research at the US National Institute on Drug Abuse (NIDA), and formerly served as the Associate Director to the Drug Czar.

Michael Walsh has been the impetus and the point man behind the push toward zero tolerance DUID legislation for some time. In November 2002, the Walsh Group partnered with the ONDCP to lobby state legislatures to replace their effect-based DUID laws with zero tolerance legislation. Then, at a joint ONDCP/NIDA conference held in February of this year, Walsh pronounced, "There is clearly a need for national leadership at the federal level to develop model statutes and to strongly encourage the states to modify their laws." Within two weeks, H.R. 3907 and H.R. 3922 were introduced in Congress to mandate states to do just that. Today, the Walsh Group remains the primary lobby and educational organization on DUID-related information, working in concert with the Drug Czar's office to promote zero tolerance DUID legislation.

The second prominent proponent of the enactment of zero tolerance DUID legislation is former 1970s Drug Czar Robert DuPont -- another ex-NIDA director who now helms the workplace drug testing consultation firm Bensinger, Dupont & Associates.35 Over the past two decades, Dupont has been a key player in the development and enactment of workplace drug testing guidelines, including the federal regulations that govern the testing of federally licensed drivers.36 Dupont is now lobbying to expand these federal guidelines to apply to all motorists. He also favors the establishment of random, roadside drug testing checkpoints.37 "We must move away from the concept of you can't drive impaired by drugs to you can't drive on drugs at all," he says, noting that drivers who test positive for drug metabolites but are otherwise unimpaired should be stripped of their license and then be monitored through regularly scheduled drug tests, including hair testing, for a period of two to five years.38 "Most people don't need [drug] treatment, they need a reason not to use drugs," and the enforcement of zero tolerance DUID legislation gives them that incentive, he believes.39

HOW TO COMBAT "ZERO TOLERANCE" DUID LEGISLATION

So now that you are aware of the background of zero tolerance DUID laws and who's campaigning for them, the next question is, how do we effectively combat this legislation?

From a legislative standpoint, it is vital that we express to politicians the fact that we, as do our opponents, strongly support the goal of keeping impaired drivers off the road -- regardless of whether the driver is impaired from alcohol or other drugs. However, zero tolerance DUID laws do little to meet this goal. Rather, they are an attempt to misuse the traffic safety laws in order to identify and prosecute recreational drug users per se by inappropriately defining sober drivers who present no traffic safety risk as legally being impaired.

By comparing zero tolerance DUID laws to our existing laws prohibiting drunk driving, their intellectual dishonesty becomes that much more apparent. Do drunk driving laws punish drivers for simply consuming alcohol? No. They sanction drivers who are impaired by alcohol to the point that they are no longer safe to operate a motor vehicle. Why not apply this same standard to DUID legislation? Do drunk driving laws target drivers for having previously consumed alcohol some days or weeks earlier? Of course not. They sanction drivers for present intoxication, and only if that intoxication is presently affecting their driving performance. Here again, why not apply this same common-sense standard to DUID legislation? Do drunk driving laws set their per se levels at zero? No, they employ scientifically sound cutoff levels that can be correlated to impairment of performance. Once again, why not apply this same standard to DUID laws?

At a minimum, state DUID laws should identify "parent drugs," not simply inactive drug metabolites. Further, these laws must employ scientifically sound cutoff levels that correlate drug concentration to impairment of performance, similar to the 0.08 BAC standard that now exists for drunk driving in most states. There must also be assurances that these laws mandate any and all drug testing to be performed and confirmed by accredited state labs using uniform procedures and standards. It is my opinion that such measures, if enacted by the states, would be a reasonable alternative to unsound "zero tolerance" drugged driving legislation.

I FOUGHT THE LAW AND THE LAW WON

Finally, if you are practicing law in a state that has already enacted zero tolerance DUID legislation, here are some suggestions on challenging the the law's enforcement.

1) Epidemiological data is lacking on the number of people who drive under the influence of controlled substances, as is any objective evidence that zero tolerance DUID laws have a deterrent effect on drivers or have led to a reduction in the number of motorists driving under the influence of drugs. In addition, according the Department of Transportation, "The role of drugs as a causal factor in traffic crashes involving drug-positive drivers is still not understood."40

2) There exists no scientific consensus on appropriate cutoff levels for detecting the presence of drugs and/or drug metabolites in bodily fluids other than urine. In particular, oral fluid assays for most drugs of abuse are still in developmental stages. As a result, "There are no nationally established standard methods for oral fluid drug testing, nor are their any certification programs currently available" to validate the accuracy of the test result.41

3) Neither the law nor the testing devices can delineate between chronic and occasional drug use. Is it appropriate to punish an occasional user the same way under the law as a chronic offender?

4) Most importantly, there exists no scientific standards correlating drug concentration to impairment of performance. There exists no known dose concentration relationship correlating drug metabolite levels in the urine or blood to impairment, nor does there exist a consensus regarding at what concentration levels the detection of a parent drug in the blood or saliva is associated with driver impairment.

5) All positive test results must be confirmed at an accredited lab for accuracy. However, most legislatures fail to appropriate funding for confirmation testing, or allow for the establishment of accredited labs to perform this testing. Non-accredited labs may use cutoff standards that vary from the national guidelines, thus bringing the accuracy of their test results into question.

6) Finally, if the presence of illicit drugs or drug metabolites were detected through the use of a rapid point-of-collection-testing (POCT) immunoassay devices (This would only apply to urine and oral collection devices.), then confirmation testing in a toxicology lab is required, as is independent verification of the initial result. (Studies have found that police officers are more likely than trained lab technicians to make "human errors" using POCT devices and interpreting the results.) Lastly, most POCT technology is not FDA approved, and thus, is open to legal challenges.


1 USA Today. "Growing danger: Drugged driving." October 21, 2004; Las Vegas Review-Journal. "Congress must address issue of drugged driving." March 21, 2004; New York Times. "Many, undetected, use drugs and then drive." November 14, 2002.

2 US Department of Transportation, National Highway Traffic Safety Administration. State of Knowledge of Drug-Impaired Driving: FINAL REPORT. September 2003.

3 Persistence of urinary marijuana metabolites after supervised abstinence in heavy, longtime users has been recorded in clinical studies for periods of 30 to 70 days. See specifically: Ellis et al. Excretion patterns of cannabinoid metabolites after last use in a group of chronic users. Clin Pharmacolo Ther. November 1985: 572-578 and Dackis et al. Persistence of urinary marijuana levels after supervised abstinence. Am J Psychiatry. September 1982: 1196-1198.

4 Arizona's law calls for mandatory imprisonment upon conviction for a first offense.

5 Georgia's law calls for mandatory imprisonment upon conviction for a first offense.

6 Iowa's law calls for mandatory imprisonment upon conviction for a first offense.

7 Michigan's law took effect in October 2003.

8 Minnesota's law exempts marijuana and marijuana metabolites, stating, "It is a crime for any person to drive, operate, or be in physical control of any motor vehicle ... when the person's body contains any amount of a controlled substance in schedule I or II other than marijuana or tetrahydrocannabinols."

9 Pennsylvania's law took effect in January 2004.

10 Utah's law calls for mandatory imprisonment upon conviction for a first offense.

11 Wisconsin's law took effect in January 2004.

12 As an analogy, think of a drug metabolite as similar to a fingerprint. Though it indicates a person was present at a certain place, it does not give specific information as to when the person was present, or why.

13 As noted by the National Institutes of Health 1997 Workshop on the Medical Utility of Marijuana, "Cannabinoid metabolism is extensive with at least 80 probably biologically inactive but not completely studied metabolites formed from THC alone."

14 As noted earlier (see footnote 3), THC's metabolites are fat soluble and may remain identifiable in urine for several days or weeks following the drug's use.

15 US Department of Justice, Bureau of Justice Statistics. Drugs, Crime, and the Justice System (NCJ-133652). December 1992.

16 US Department of Transportation, National Highway Traffic Safety Administration. State of Knowledge of Drug-Impaired Driving: FINAL REPORT.

17 Yale Caplan. "Technology for Testing Drugs of Abuse in DUID." In: Developing Global Strategies for Identifying, Prosecuting, and Treating Drug-Impaired Drivers: Symposium Report. June 2004.

18 See footnote 15.

19 Yale Caplan. "Technology for Testing Drugs of Abuse in DUID."

20 US Department of Transportation, National Highway Traffic Safety Administration. State of Knowledge of Drug-Impaired Driving: FINAL REPORT.

21 Ibid. Figure 3-1: Drug Detection Periods In Various Specimens; See also: Huestis et al. Relationship of (9)-tertrahydrocannabinol concentrations in oral fluid and plasma after controlled administration of smoked cannabis. J Anal Toxicol. September 2004: 394-399.

22 US Department of Transportation, National Highway Traffic Safety Administration. State of Knowledge of Drug-Impaired Driving: FINAL REPORT.

23 Drummer et al. The involvement of drugs in drivers killed in Australian road traffic crashes. Accid Anal Prev. 2004: 239-248

24 Grotenhermen et al. Developing per se laws for driving under the influence of cannabis (DUIC). Paper presented at the 17th International Conference on Alcohol, Drugs and Traffic Safety. August 10, 2004.

25 US Department of Transportation, National Highway Traffic Safety Administration. State of Knowledge of Drug-Impaired Driving: FINAL REPORT. Figure 3-1: Drug Detection Periods In Various Specimens; See also: Dolan et al. An overview of the use of hair, sweat and saliva to detect drug use. Drug Alcohol Rev. 2004: 213-217 and Verstraete. Detection times of drugs of abuse in blood, urine and oral fluid. Ther Drug Monit. 2004: 200-205.

26 US Department of Transportation, National Highway Traffic Safety Administration. State of Knowledge of Drug-Impaired Driving: FINAL REPORT.

26 US Department of Transportation, National Highway Traffic Safety Administration. State of Knowledge of Drug-Impaired Driving: FINAL REPORT.

27 Spiehler et al. Analysis of Drugs in Saliva. In: Forensic Science: On-Site Drug Testing. D Humana Press Inc. (publication date unknown)

28 Developing Global Strategies for Identifying, Prosecuting, and Treating Drug-Impaired Drivers: Symposium Report. June 2004.

29 Studies include: Canadian Special Senate Committee on Illegal Drugs. Cannabis: Our Position for a Canadian Public Policy. 2002: See specifically Chapter 5: "Driving Under the Influence of Cannabis;" UK Department of Environment, Transport and the Regions (Road Safety Division). Cannabis and Driving: A Review of the Literature and Commentary. 2000; Allison Smiley. Marijuana: On-Road and Driving Simulator Studies. In: H. Kalant et al. (Eds) The Health Effects of Cannabis. Toronto: Center for Addiction and Mental Health. 1999: 173-191.

30 Sexton et al. The influence of cannabis on driving: A report prepared for the UK Department of the Environment, Transport and the Regions (Road Safety Division). 2000; UK Department of Environment, Transport and the Regions (Road Safety Division). Cannabis and Driving: A Review of the Literature and Commentary; 2000; Allison Smiley. Marijuana: On-Road and Driving Simulator Studies.

31 Chesher et al. 2002 Cannabis and alcohol in motor vehicle accidents. In: Grotenhermen and Russo (Eds) Cannabis and Cannabinoids: Pharmacology, Toxicology, and Therapeutic Potential. New York: Haworth Press. pp. 313-323.

32 Ibid.; Allison Smiley. Marijuana: On-Road and Driving Simulator Studies; 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.”

33 Canadian Special Senate Committee on Illegal Drugs. 2002. Cannabis: Our Position for a Canadian Public Policy.

34 http://www.walshgroup.org

35 http://www.bensingerdupont.com

36 These guidelines subject licensed commercial drivers to submit to random urinalysis for the purpose of screening for illicit drug metabolites. These regulations also establish per se guidelines for drug metabolites, although these cutoff levels are admittedly not correlated to impairment.

37 Robert Dupont. "Drugs and driving." Letter to the editor: USA Today. October 28, 2004.

38 Robert Dupont. "Conviction is an Opportunity for Intervention." In: Developing Global Strategies for Identifying, Prosecuting, and Treating Drug-Impaired Drivers: Symposium Report. June 2004.

39 Ibid.

40 US Department of Transportation, National Highway Traffic Safety Administration. State of Knowledge of Drug-Impaired Driving: FINAL REPORT.

41 Ibid.