DRUG-IMPAIRED 

DRIVING

Additional Support 

Needed for Public 

Awareness Initiatives

Report to Congressional Committees

February 2015

GAO-15-293

United States Government Accountability Office
United States Government Accountability Office

Highlights of GAO-15-293, a report to 

congressional committees

February 2015

DRUG-IMPAIRED DRIVING

Additional Support Needed for Public Awareness 

Initiatives

Why GAO Did This Study

The issue of alcohol-impaired driving 

has received broad attention over the 

years, but drug-impaired driving also 

contributes to fatalities and injuries 

from traffic crashes. However, 

knowledge about the drug-impaireddriving problem is less advanced than 

for alcohol-impaired driving. 

Through Senate Report No. 113-45 

(2013), Congress required GAO to 

report on the strategies NHTSA, 

ONDCP, and states have taken to 

address drug-impaired driving and 

challenges they face in detecting and 

reducing such driving. This report 

discusses (1) what is known about the 

extent of drug-impaired driving in the 

United States; (2) challenges that exist 

for federal, state, and local agencies in 

addressing drug-impaired driving; and 

(3) actions federal and state agencies 

have taken to address drug-impaired 

driving and what gaps exist in the 

federal response. GAO reviewed 

literature to identify sources of data on 

drug-impaired driving; reviewed 

documentation and interviewed 

officials from NHTSA, ONDCP, and 

HHS; and interviewed officials from 

relevant advocacy and professional 

organizations and seven selected 

states. States were selected based on:

legal status of marijuana, proximity to 

states with legalized marijuana, and

drugged-driving laws.

What GAO Recommends

GAO recommends that NHTSA take 

additional actions to support states in 

emphasizing to the public the dangers 

of drug-impaired driving. DOT agreed 

with GAO’s recommendation.

What GAO Found

Various state and national-level data sources—including surveys, arrest data, 

drug-testing results, and crash data—provide limited information on the extent of 

drugged and drug-impaired driving in the United States. For example, based on

preliminary results from a representative sample of weekend-nighttime and 

Friday daytime drivers, the National Highway Traffic Safety Administration’s 

(NHTSA) 2013-2014 National Roadside Survey of Alcohol and Drug Use by 

Drivers (NRS) estimated that 20 percent of drivers would have tested positive for 

at least one drug, with marijuana being the most common drug. However, the 

survey does not capture the extent to which drivers were impaired by drugs. 

Arrest data and drug-testing results provide some information on drug-impaired 

driving, but these data are limited. For example, data for drug impairment may 

not be separated from that for alcohol impairment and drug testing is not 

standardized. According to NHTSA officials, currently available data on drug

involvement in crashes are generally unreliable due to variances in reporting and 

testing.

The lack of a clear link between impairment and drug concentrations in the body

makes it difficult to define drug impairment, which, in turn, exacerbates 

challenges related to enforcement and public awareness. Compared to alcohol, 

defining and identifying impairment due to drugs is more complicated due to the 

large number of available drugs and their unpredictable effects. For example, the 

NRS includes tests for 75 illegal prescriptions, and over-the-counter (OTC) drugs 

identified as potentially impairing. Additionally, law enforcement processes for 

obtaining samples for drug testing can be time consuming and result in a loss of 

evidence. For example, there is no validated device for roadside drug testing, 

and obtaining a search warrant to collect a blood sample to confirm the presence 

of drugs in a driver’s system could take several hours, during which time the 

concentration of the drug in the driver’s system could dissipate. Further, state 

officials identified limited public awareness about the dangers of drugged driving

as a challenge. As a result, members of the public may drive while impaired 

without knowing the risks, potentially leading to collisions, injuries, and fatalities.

Federal and state agencies—including NHTSA, the White House Office of 

National Drug Control Policy (ONDCP), and the Department of Health and 

Human Services (HHS)—are taking actions to address drug-impaired driving, 

including improvements in the areas of research and data, education for police 

officers, evidence gathering, and legal changes. For example, NHTSA is 

currently conducting research to assess the crash risk associated with drug use 

(including illegal, prescription, and OTC drugs) by collecting samples from more 

than 10,000 drivers. However, public awareness of the dangers of drug-impaired 

driving is an area in which state officials told us that NHTSA could do more to

support their efforts. As part of its mission to support state safety efforts, NHTSA 

has provided media and other materials to states for impaired-driving awareness 

programs, but these materials are focused on alcohol-impaired driving. While 

NHTSA plans to improve public awareness through initiatives to conduct surveys 

on drug-impaired-driving behaviors and attitudes as well as training for medical 

professionals, these plans could take several years to implement. Additional 

efforts, such as general messaging reminding the public about the impairing 

effects of drugs, could help improve public awareness in the near term.

View GAO-15-293. For more information, 

contact Susan Fleming, at (202) 512-2834 or 

flemings@gao.gov
Page i GAO-15-293 Drug–Impaired Driving

Letter 1

Background 3

Limited Data Exists on the Extent of Drug-Impaired Driving in the 

U.S. 6

Difficulty of Defining Drug Impairment Exacerbates Challenges 

Related to Enforcement and Public Awareness 15

Federal and State Agencies Are Working to Address DrugImpaired Driving, but NHTSA’s Efforts to Improve Public 

Awareness Have Been Limited 21

Conclusions 32

Recommendation 32

Agency Comments 33

Appendix I Objectives, Scope, and Methodology 34

Appendix II Comments from the Department of Transportation 37

Appendix III GAO Contact and Staff Acknowledgments 39

Tables

Table 1: Most Common Drugs Found in Test Results for Drivers, 

2007 and 2012 8

Table 2: Impaired Driving Enforcement in Arizona, 2005–2013 12

Table 3: Comparison of Examples of Possible Alcohol and DrugImpairment Symptoms 18

Figures

Figure 1: NHTSA “Drive Sober or Get Pulled Over” and “Buzzed 

Driving is Drunk Driving” Campaigns 20

Figure 2: Map of States with Zero Tolerance Per Se Laws and 

Per Se Laws Based on Drug Concentration Limits, as of 

December 2014 28

Contents
Page ii GAO-15-293 Drug–Impaired Driving

Abbreviations

ARIDE Advanced Roadside Impaired Driving Enforcement

BAC blood-alcohol concentration

CDC Centers for Disease Control and Prevention

DOJ Department of Justice

DRE Drug Recognition Expert

DUI driving under the influence of alcohol and/or drugs

DUID driving under the influence of drugs

FARS Fatality Analysis Reporting System

FDA Food and Drug Administration

GHSA Governors Highway Safety Association

HHS Department of Health and Human Services

IACP International Association of Chiefs of Police

JOL Judicial Outreach Liaison

MADD Mothers Against Drunk Driving

MAP-21 Moving Ahead for Progress in the 21st Century Act

NCSL National Conference of State Legislatures

NHTSA National Highway Traffic Safety Administration

NIDA National Institute on Drug Abuse

NIH National Institutes of Health

NRS National Roadside Survey of Alcohol and Drug Use 

by Drivers

NSDUH National Survey on Drug Use and Health

NTSB National Transportation Safety Board

ONDCP Office of National Drug Control Policy

OTC over-the-counter

PIRE Pacific Institute for Research and Evaluation

SAMHSA Substance Abuse and Mental Health Services 

Administration

SOFT Society of Forensic Toxicologists, Inc.

THC tetrahydrocannabinol

TSRP Traffic Safety Resource Prosecutor

This is a work of the U.S. government and is not subject to copyright protection in the 

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Page 1 GAO-15-293 Drug–Impaired Driving

441 G St. N.W.

Washington, DC 20548

February 24, 2015

The Honorable Susan Collins

Chairman

The Honorable Jack Reed

Ranking Member

Subcommittee on Transportation, Housing and Urban Development, and 

Related Agencies

Committee on Appropriations

United States Senate

The Honorable Mario Diaz-Balart

Chairman

The Honorable David Price

Ranking Member

Subcommittee on Transportation, Housing and Urban Development, and 

Related Agencies

Committee on Appropriations

House of Representatives

While the issue of alcohol-impaired driving has received broad attention 

over the years, drug-impaired driving also contributes to fatalities and 

injuries from traffic crashes. However, knowledge about the nature of the 

drug-impaired driving problem is significantly less advanced than for 

alcohol-impaired driving. Based on preliminary results from a nationally 

representative sample in 2013-2014, an estimated 20 percent of nighttime 

weekend drivers would have tested positive for illegal, prescription, or 

over-the-counter (OTC) drugs that have been identified as potentially 

impairing.1

 1

A. Berning, R. Compton, and K. Wochinger, Results of the 2013-2014 National Roadside 

Survey of alcohol and drug use by drivers (Traffic Safety Facts Research Note. Report No. 

DOT HS 812 118, U.S. Dept. of Transportation, National Highway Traffic Safety 

Administration, Washington, D.C.: 2015). These results are an estimate of the prevalence 

of drivers with detectable amounts of drugs in their systems and do not imply impairment.

The National Roadside Survey is a survey sponsored by the National Highway Traffic 

Safety Administration that indicates the extent to which people drive with drugs present in 

their system, and is representative of the United States. This survey was conducted in 

2013-2014, with full results expected in 2015.

The White House’s Office of National Drug Control Policy 

(ONDCP) has identified “drugged driving” as a policy priority, and 

established a goal in the agency’s 2011 National Drug Control Strategy to 
Page 2 GAO-15-293 Drug–Impaired Driving

reduce drugged driving 10 percent by 2015.2

The Senate Report accompanying the Transportation and Housing and 

Urban Development, and Related Agencies Appropriations Bill, 2014 

required GAO to report on the strategies that NHTSA, ONDCP, and 

states have taken to address drug impairment and the challenges faced 

in detecting and reducing drug-impaired driving.

The National Highway 

Traffic Safety Administration (NHTSA) assists states in implementing 

programs to address impaired driving—including those aimed at reducing 

drug-impaired driving—and has funded research examining the extent 

and nature of drug-impaired driving as well as the effectiveness of 

countermeasures.

3

This report uses the term “drug-impaired driving” to refer to driving while 

impaired by illegal drugs or prescription and OTC (legal) medications. For 

this work, we conducted a literature search to identify sources of data and 

studies on the issue and extent of drug-impaired driving, reviewed these 

data and studies, and determined their limitations. Additionally, we 

reviewed documentation and interviewed officials from seven federal 

agencies: NHTSA; ONDCP; National Transportation Safety Board 

(NTSB); Department of Health and Human Services (HHS) and 

component agencies including the Substance Abuse and Mental Health 

Services Administration (SAMHSA), Centers for Disease Control and 

Prevention (CDC), Food and Drug Administration (FDA), and National 

Institutes of Health (NIH).

This report discusses 

(1) what is known about the extent of drug-impaired driving in the United 

States; (2) challenges that exist for federal, state, and local agencies in 

addressing drug-impaired driving; and (3) actions federal and state 

agencies have taken to address drug-impaired driving and gaps that exist 

in the federal response to drug-impaired driving.

4

 2

For the purposes of this report, the term “drugged driving” refers to driving with any 

detectable amount of drugs in one’s system, as opposed to “drug-impaired driving,” which 

refers to driving while impaired to some degree from using drugs. ONDCP’s goal is to 

reduce the prevalence of drugged driving by 10 percent as compared to a 2009 baseline, 

established by the Department of Health and Human Services’ Substance Abuse and 

Mental Health Services Administration’s 2009 National Survey on Drug Use and Health.

We also reviewed documentation obtained 

3

S. Rep. No.113-45 (2013).

4

Within NIH, the National Institute on Drug Abuse (NIDA) is the primary institute involved 

in this topic. NIDA is one of the 27 institutes and centers within the National Institutes of 

Health.
Page 3 GAO-15-293 Drug–Impaired Driving

from and interviewed officials with responsibilities related to drug-impaired 

driving, such as traffic safety, toxicology lab, and law enforcement 

officials, in seven states (Arizona, California, Colorado, Kansas, Ohio, 

Vermont, and Washington). We selected these states based on 

recommendations from federal officials and representatives from 

advocacy and professional organizations and to represent a variety of 

laws, programs, and other factors. Our selection included:

• states with legalized recreational marijuana,

• states that geographically border states in which recreational 

marijuana use is legal,

• states with legalized medical marijuana,

• states representing a variety of drug-impaired driving laws, and

• states identified as having robust programs dealing with driving under 

the influence of drugs.

We also reviewed documentation and interviewed representatives from 

advocacy and professional organizations, including the Governors 

Highway Safety Association (GHSA), National District Attorneys 

Association, Society of Forensic Toxicologists, Inc. (SOFT), Mothers 

Against Drunk Driving (MADD), International Association of Chiefs of 

Police (IACP), Insurance Institute for Highway Safety, and National 

Conference of State Legislatures (NCSL). See additional information on 

our scope and methodology in appendix I.

We conducted this performance audit from April 2014 through February 

2015 in accordance with generally accepted government auditing 

standards. Those standards require that we plan and perform the audit to 

obtain sufficient, appropriate evidence to provide a reasonable basis for 

our findings and conclusions based on our audit objectives. We believe 

the evidence obtained provides a reasonable basis for our findings and 

conclusions based on our audit objectives.

Similar to drunk driving, drug-impaired driving can result in crashes 

leading to death or injury of vehicle occupants and pedestrians, along 

with other safety and traffic issues for individuals and society. Taking into 

consideration these possible harms, Congress has authorized grant 

funding to states to combat impaired driving through transportation 

legislation—most recently the Moving Ahead for Progress in the 21st 

Background
Page 4 GAO-15-293 Drug–Impaired Driving

Century Act (MAP-21).5 These grant programs are designed to 

encourage states to adopt and implement effective programs to reduce 

driving under the influence of alcohol, drugs, or the combination of alcohol 

and drugs. Historically, these programs have been focused on reducing 

alcohol-impaired driving. For example, in the late 1990s, Congress made 

grant funds available to states to encourage them to lower the illegal per 

se driving blood-alcohol concentration (BAC) limit to 0.08.6

NHTSA administers grant programs for safety initiatives to assist states in 

their efforts to reduce traffic-related fatalities, including fatalities involving 

drug- and alcohol-impaired driving. NHTSA also provides guidance and 

technical assistance to states, and conducts research on drivers’ behavior 

and traffic safety. As part of such research, NHTSA works with traffic 

safety organizations, such as GHSA and MADD, and other federal 

agencies, such as ONDCP. In addition to NHTSA, other federal agencies 

conduct research and implement programs that, in whole or in part, seek 

to increase knowledge about the problem of drug-impaired driving and to 

identify and implement policies and programs to reduce drug-impaired 

driving. These agencies include ONDCP; HHS’s SAMHSA, NIH, FDA, 

and CDC; Department of Justice (DOJ); and NTSB.

In other 

words, with respect to a BAC limit of 0.08, anyone whose blood contains 

8/100th of 1 percent of alcohol (or higher) would be deemed to be driving 

while intoxicated. All 50 states and the District of Columbia have 0.08 

laws as well as laws making it illegal to drive while impaired by drugs.

Drug-impaired driving may be caused by use of illegal drugs, legally 

prescribed or OTC drugs that are misused, and some legally prescribed 

 5

Under MAP-21, 52.5 percent of the total amount of National Priority Safety Program 

funds are available for impaired-driving countermeasures, with up to 15 percent of those 

funds available for incentive grants for ignition interlocks—devices that prevent drivers 

from starting their cars if they have been drinking alcohol. Any of the remaining funding is 

available for other impaired-driving countermeasures, funding that is allocated to states for 

eligible impaired-driving activities, including countermeasures for alcohol- and drugimpaired driving. Pub. L. No. 112-141, § 31105(a), 126 Stat. 405, 748 (2012). MAP-21 

expired September 30, 2014. Programs and budget authority authorized under MAP-21 

were extended until May 31, 2015 by Pub. L. No. 113-159,128 Stat. 1839 (2014). The 

National Priority Safety Programs were authorized $181,084,932 for the period between 

October 1, 2014, and May 31, 2015.

6

“Per se BAC laws” establish the BAC level at which it is illegal per se (in itself) for a driver 

to operate a vehicle, regardless of the driver’s apparent condition or actions. 
Page 5 GAO-15-293 Drug–Impaired Driving

or OTC drugs even when used as intended.7 While 23 states and the 

District of Columbia have legalized the use of marijuana for medical 

purposes, according to the NCSL, and two states—Colorado and 

Washington—allow the use of marijuana for recreational purposes, the 

federal government continues to consider marijuana as an illegal drug, 

with no medical use.8

For the purposes of this report, we have used the following terminology:

Throughout the report, we have noted instances in 

which data may include marijuana as either a legal or illegal drug. 

According to the FDA, some prescription and OTC drugs can impair 

driving ability, while others have no effect or can even enable patients to 

drive more safely.

• Drugged driving: driving with the presence of drugs in one’s system 

regardless of impairment.

• Drug-impaired driving: driving with a diminished ability to operate a 

vehicle due to drug use.

• Drug test: the toxicological analysis of a biological specimen—blood, 

urine, or oral fluid (saliva)—to determine the presence or absence of 

specific drugs or their metabolites.

• DUI: driving under the influence of alcohol and/or drugs.

• DUID: driving under the influence of drugs.

• Impairment: a diminished ability to perform specific functions.

• Metabolites: the products of drug metabolism found in bodily fluids, 

which indicate prior drug use.

• Tetrahydrocannabinol (THC): the main psychoactive compound 

found in the cannabis (marijuana) plant.

 7

Over-the-counter drugs are those that can be purchased without a doctor’s prescription, 

including some pain-relievers, cold and cough medicines, and others. 

8

In November 2014, ballot initiatives legalizing recreational marijuana passed in Alaska, 

Oregon, and the District of Columbia; these initiatives have not taken effect as of the 

beginning of February 2015.
Page 6 GAO-15-293 Drug–Impaired Driving

• Toxicology: the study of the effects of drugs—whether illegal, 

prescription, or over-the-counter—on humans.

Drugs may be categorized in several ways including by the chemical type 

or by the way the drug is used. For example, this report uses the following 

terms to classify drugs, among others:

• Antidepressants: drugs used to treat depression and other 

conditions, including anxiety disorders.

• Cannabinoids: compounds contained in marijuana.

• Narcotics: drugs including opium and those derived from it, such as 

heroin and codeine.

• Depressants: drugs that inhibit the activity of the brain and may result 

in muscle relaxation, lowered blood pressure and heart rate, and 

slowed breathing; includes anxiety and seizure medications.

• Stimulants: drugs that may result in increased alertness and elevated 

heart rate and respiration; includes cocaine and amphetamines.

• Synthetics: synthetic drugs, as opposed to natural drugs such as 

marijuana, are chemically produced in a laboratory to mimic the 

effects of other drugs. Synthetic drugs may be developed in order to 

circumvent existing drug laws. Examples include synthetic 

cannabinoids and cathinones.

There is no national source of data on the extent of drug-impaired driving 

in the United States, but various state and national sources of data on 

drugged driving can provide limited information on the extent to which 

drivers in the United States have drugs in their systems. For example, 

national and state roadside surveys provide information on the 

prevalence of drugged driving in respective survey areas. Other sources 

of data provide some information on drugged and drug-impaired driving, 

such as surveys on self-reported drugged-driving behavior, impaireddriving arrests and toxicology results, and crash data.9

 9

Toxicology results are the result of laboratory testing of biological samples of bodily fluid 

for the presence of various substances.

However, 

Limited Data Exists 

on the Extent of DrugImpaired Driving in 

the U.S.
Page 7 GAO-15-293 Drug–Impaired Driving

limitations to the currently available data include underreporting and a 

lack of centralization or standardization in reporting.

National and state roadside surveys provide data on the prevalence of 

drugged driving in statistically representative samples of drivers. For 

example, NHTSA’s 2007 National Roadside Survey of Alcohol and Drug 

Use by Drivers (NRS) provides information on drivers testing positive for 

illegal, prescription, and OTC drugs in a nationally representative sample 

of weekend-nighttime and Friday daytime drivers.10 Based on the 2007 

survey, NHTSA estimated that 16.3 percent of nighttime drivers 

nationwide would have tested positive for at least one drug, with 

marijuana being the most common drug found in test results (see table 1). 

While NRS survey data provides useful information on the estimated 

prevalence of drugged driving, these results do not measure the extent to 

which drivers are impaired by the drugs in their systems as the presence 

of drugs or drug metabolites does not necessarily indicate impairment. 

For example, marijuana metabolites can be detected in blood samples 

several weeks after daily users’ last use. Nonetheless, the 2007 NRS

provided the first objective data on drug use among drivers in the United 

States and, according to officials at the National Institute on Drug Abuse

(NIDA) and SOFT, served as a wake-up call regarding the extent of 

drugged-driving in the United States. According to NHTSA, the survey 

was repeated in 2013-2014 following the same general methodology as 

the 2007 survey and results will be available in 2015. Preliminary results 

from that survey estimated that 20 percent of nighttime weekend drivers 

would have tested positive for illegal, prescription, or OTC drugs that 

have been identified as potentially impairing.11

 10

An assessment of trends 

in drugged driving in the United States may be feasible as future results 

beyond the 2013-2014 NRS become available. Table 1 shows additional 

drug test results from this survey.

Lacey et al. The NRS methodology involves randomly stopping drivers at locations 

across the United States to conduct voluntary surveys and collect biological samples after 

obtaining consent. Drivers who participated were tested for illegal, prescription, and OTC 

drugs through analyses of oral fluid, blood, and breath specimens taken during key 

periods during which impaired driving most often occurs. Drugs tested were chosen in part 

due to their potential to impair driving performance. 

11A. Berning, R. Compton, and K. Wochinger, Results of the 2013-2014 National 

Roadside Survey.

Survey Data on 

Prevalence of Drugged 

Driving
Page 8 GAO-15-293 Drug–Impaired Driving

Table 1: Most Common Drugs Found in Test Results for Drivers, 2007 and 2012

2007 National 

Roadside Survey

2012 California 

Roadside Survey a

Marijuana 

b

6.8% 5.5%

Stimulants 3.2% 3.2%

Poly-Use (more than one class of drug) 2.8% 3%

Narcotic-Analgesics 1.6% 1.1%

Sedatives 0.8% 0.7%

Antidepressants 0.7% 0.2%

Other 0.3% 0.3%

Total 16.3% 14%

Sources: National Highway Traffic Safety Administration’s (NHTSA) 2007 National Roadside Survey of Alcohol and Drug Use by 

Drivers: Drug Results (NRS) and Results of the 2012 California Roadside Survey of Nighttime Weekend Drivers’ Alcohol and Drug Use. 

| GAO-15-293

a

During daytime Friday times, drivers were tested for the presence of drugs using oral fluid. During 

nighttime weekend times, drivers were tested for the presence of drugs using oral fluid and blood. A 

positive test for either oral fluid or blood is a positive drug test.

b

During nighttime weekend times, drivers were tested for the presence of drugs using oral fluid. A 

positive oral fluid test is a positive drug test.

California’s Office of Traffic Safety found results similar to the 2007 NRS

during its 2012 California Roadside Survey of Nighttime Weekend 

Drivers’ Alcohol and Drug Use (see table 1).12

 12Lacey, John H; Kelley-Baker, Tara, et. Al, 2012 California Roadside Survey of Nighttime 

Weekend Drivers’ Alcohol and Drug Use (Pacific Institute for Research and Evaluation, 

Calverton, MD: 2012).

Specifically, 14 percent of 

nighttime weekend drivers tested positive for at least one drug, with 

marijuana being the most frequent drug identified. Additionally, the 

Washington Traffic Safety Commission has commissioned the first of two 

roadside surveys, using what NHTSA describes as comparable 

methodology to the 2007 NRS, meant to measure drug and alcohol use 

among drivers before and after implementation of the 2012 state law 

legalizing recreational marijuana use. Results from the survey are 

expected in 2015.
Page 9 GAO-15-293 Drug–Impaired Driving

The NRS and California surveys also collected self-reported data on drug 

use among drivers who participated in the survey.13

• an estimated 7.5 percent of nighttime weekend drivers testing positive 

for cocaine reported they had used cocaine in the past 24 hours,

For instance, during 

the California Survey, approximately 14 percent of all drivers who 

reported having used marijuana in the past reported having used it within 

2 hours of driving in the past year. In the NRS, all drivers who provided an 

oral fluid sample were asked to report if they had used a drug before 

driving and, if so, what type. For the subset of Friday and nighttime 

weekend drivers who tested positive for at least one drug based on the 

oral fluid sample, the drivers’ answers regarding prior drug use were 

compared to positive oral fluid-analysis results to determine agreement 

between self-reported behavior and the oral fluid test. Results of this 

comparison include:

• an estimated 25.7 percent of nighttime weekend drivers testing 

positive for marijuana reported they had used marijuana in the past 24 

hours,

• an estimated 59.9 percent of nighttime weekend drivers testing 

positive for pain medication reported they had used pain medication in 

the past 24 hours, and

• an estimated 66.4 percent of nighttime weekend drivers testing 

positive for antidepressants reported they had used antidepressants 

in the past 24 hours.

Agreement between reported drug use in the past 24 hours and positive 

oral-fluid-analysis results for the nighttime-driving samples was greatest 

among users of antidepressants, cough suppressants, and pain 

medications and lowest for amphetamines and barbiturates.14

 13NRS respondents completed a paper-and-pencil, drug-use-disorder screening 

instrument. In the 2013 NRS, in addition to an oral fluid test, the driver was asked 

additional questions about prescription drug use. For the California survey, respondents 

were asked questions covering drug use. 

While selfreported data may be useful in tracking trends in reported drug use and 

attitudes about drugged driving, the NRS methodology noted that it may 

14These findings may be in part due to the fact that some drugs, such as marijuana, 

remain detectable in human fluids for days or weeks after they have been ingested 

Surveys on Drug Use 

Behavior
Page 10 GAO-15-293 Drug–Impaired Driving

under-report actual activity and therefore be insufficient for estimating the 

extent of drugged driving.

Additional studies compile self-reported data on attitudes and behaviors 

regarding drug use and driving, which may be helpful in tracking trends in 

behavior. SAMHSA’s National Survey on Drug Use and Health (NSDUH) 

is an annual survey of a nationally representative sample of the United 

States population.15 The NSDUH includes questions specific to driving 

while under the influence of illegal drugs. According to this survey, driving 

under the influence of illegal drugs is most common in respondents aged 

18–25 (an estimated 10.6 percent in 2013, the latest survey results 

available). Overall, the percentage of respondents aged 12 or older who 

report driving under the influence of illegal drugs in the past year has 

been around 4 percent from 2008 through 2012.16 NIH’s NIDA also 

supports various studies on drug use including the College Life Study on 

health-related behaviors of college students, and Monitoring the Future, 

which measures attitudes of adolescents related to drug and alcohol 

use.17 According to the 2012 Monitoring the Future Survey, an estimated 

10.6 percent of high school seniors drove a car, truck, or motorcycle in 

the prior 2 weeks after having smoked marijuana.18

 15Substance Abuse and Mental Health Services Administration, Results from the 2012 

National Survey on Drug Use and Health: Summary of National Findings, NSDUH Series 

H-46, HHS Publication No. (SMA) 13-4795 (Rockville, MD: 2013).

16From 2008 to 2012, the percentage of respondents reporting driving under the influence 

of drug varied from 3.7 to 4.2 percent, but due to sampling error the actual differences 

from year to year may be insignificant. Respondents to the survey are age 12 and older. 

17NIDA’s College Life Study is a longitudinal study of 1,253 college students at a large, 

public, mid-Atlantic university aimed at discovering the impact of health-related behaviors 

during the college experience. 

18Bachman, J. G., Johnston, L. D., and O’Malley, P. M., Monitoring the Future: 

Questionnaire responses from the nation’s high school seniors, 2012 (Institute for Social 

Research, Ann Arbor, MI: 2014). The 2012 Monitoring the Future survey provides 

estimates for a nationally representative sample of high school seniors on an annual 

basis. The survey does not include in its target population those who drop out of high 

school before the last few months of their senior year, and so excludes a relatively small 

proportion of each age cohort, but may disproportionately exclude those who have a 

tendency toward certain behaviors such as illegal drug use. The overall student response 

rate for 2012 was reported to be 83 percent.
Page 11 GAO-15-293 Drug–Impaired Driving

Data on drug-impaired driving arrests and toxicology results in our seven 

selected states provide some information on drug-impaired driving, but 

are limited by a lack of separation of data from driving under the influence 

(DUI) arrests, underreported instances of drug-impaired driving, 

decentralized reporting, and a lack of standardization in drug testing. For 

example, officials in six of the seven selected states told us that state 

arrest data does not currently separate data on drug-impaired driving and 

alcohol-impaired driving cases across law enforcement agencies. Officials 

from California stated that although the state recently revised its vehicle 

code to delineate DUI into three separate reportable sections, it could be 

several years until any data generated from the new system can be 

considered complete and accurate.19 Arizona’s Governor’s Office of 

Highway Safety tracks arrests for driving under the influence of alcohol 

and drugs separately, and data show an increase in drug-impaired driving 

arrests in the past 5 years, but this rise does not necessarily indicate an 

increase in drug-impaired driving. For example, Arizona data show a 966 

percent increase in drug-impaired driving arrests from 2005 through 2013. 

However, the increase in arrests may be due to the 659 percent increase 

in the number of officers participating in impaired-driving enforcement 

activities, the 1,604 percent increase in the number of traffic stops, and 

better reporting of those traffic stops, rather than an increase in drugimpaired driving. The rates of contacts resulting in DUID arrests do not 

show an increasing trend. See table 2.

 19The California vehicle code is now composed of separate reportable sections on DUI 

alcohol, DUI Drugs, and DUI Combination alcohol and drugs. 

Data on Impaired-Driving 

Arrests and Toxicology 

Results
Page 12 GAO-15-293 Drug–Impaired Driving

Table 2: Impaired-Driving Enforcement in Arizona, 2005–2013

2005 2006 2007 2008 2009 2010 2011 2012 2013

Contacts (All traffic stops) 49,230 72,057 112,555 96,243 148,063 228,146 702,921 877,617 838,979

DUI alcohol arrests 6,501 6,847 10,133 10,409 14,154 19,482 31,561 32,174 31,891

DUI drug arrests 424 541 538 694 1,153 1,679 3,579 4,511 4,519

Officers working on DUI 

enforcement activities

6,081 a 6,522 11,483 10,225 15,809 34,300 47,927 51,654 46,139

Contacts that result in DUI drug arrests .86% .75% .47% .72% .78% .74% .51% .51% .54%

Source: GAO analysis of Arizona Governor’s Office of Highway Safety data. | GAO-15-293

a

Note: Driving under the influence of alcohol or drugs is referred to as DUI. This data does not include 

impaired driving enforcement conducted by a small number (about 2 percent) of agencies that do not 

submit data.

Officers working on DUI enforcement activities is a cumulative figure: these numbers do not 

necessarily represent unique officers.

In addition, drug-impaired driving may be underreported as drivers 

impaired by both alcohol and drugs will likely be tested and prosecuted 

only for alcohol impairment because, according to officials from NHTSA 

and six of the seven selected states, evidence collection and prosecution 

are much easier for alcohol-impaired driving. Officials from NHTSA and 

six states said that in general, if a person suspected of impaired driving 

has a BAC over 0.08, the individual is not tested further for the presence 

of drugs, regardless of whether drug impairment is also suspected. As a 

result, drivers impaired by both drugs and alcohol may not be reported 

accurately in arrest data, contributing to a lack of knowledge about the 

number of drivers impaired by both drugs and alcohol.

Further, based on our review of information from the seven selected 

states on arrests and toxicology results for DUID cases, we found that 

state data on impaired driving are often not centralized or complete. 

Among the selected states, data on DUID arrests are generally collected 

by local law enforcement agencies, and one of the seven selected states 

collects statewide data on DUIDs in a centralized database. While 

Arizona collects arrest data from a majority of its local law enforcement 

agencies in a central database, a small number of local agencies do not 

participate. One official estimated about 2 percent of agencies do not 

submit data. Similarly, statewide toxicology/drug-testing data may not be 

easily available because it is decentralized. In five of the seven selected 

states, toxicology data are maintained by individual state and local law 

enforcement agencies and toxicology labs (including private and public 

labs), with no centralized database. For example in California, DUID 

testing varies by jurisdiction and can be completed by one of 22 private 
Page 13 GAO-15-293 Drug–Impaired Driving

labs or 6 public labs at the local or state level. In contrast, Vermont and 

Washington have centralized results of all DUID drug tests, which are 

conducted by a single laboratory for each state. While Vermont toxicology 

data do not show any clear trends, a study using Washington state 

toxicology data indicates that the prevalence of marijuana in suspected 

impaired-driving cases increased after marijuana was legalized, from an 

average of 19.1 percent of cases positive for tetrahydrocannabinol 

(THC) from 2009 through 2012 to 24.9 percent in 2013 (post 

legalization).20

Further, drug test results may not be comparable among laboratories. 

Officials from three of the seven selected states, as well as 

representatives from SOFT, stated that a lack of standardization among 

labs means that test results from different labs cannot necessarily be 

compared. For example, labs do not have uniform reporting-level cutoffs 

for drugs (the level at which a drug is reported as present). Therefore, for 

the same sample, one lab may report the sample as positive for the 

presence of a drug while another lab may report the sample as negative 

because the amount present is below the reporting level cutoff for the 

second lab. According to officials from HHS, while there are federal 

standards for forensic toxicology testing for federal agencies and states 

may establish standards for forensic testing, there are currently no federal

However, according to one of the authors, it is unclear 

whether this increase is due to factors other than an increase in 

marijuana-impaired driving, such as an increased focus on marijuana 

impairment in the state. Over the same period, the prevalence of alcohol 

and drugs other than marijuana in the population of suspected impaired 

drivers remained relatively stable in Washington.

 20Couper, Fiona; Peterson, Briana, “The Prevalence of Marijuana in Suspected Impaired 

Driving Cases in Washington State,” Journal of Analytical Toxicology, 18-Mar (2014). 

Tetrahydrocannabinol (THC) is the main psychoactive compound found in the cannabis 

(marijuana) plant.
Page 14 GAO-15-293 Drug–Impaired Driving

laboratory certification requirements for forensic laboratories conducting 

toxicology testing for state and local law-enforcement agencies.21

Despite these limitations, drug testing results for DUID cases can provide 

information on the types and amounts of drugs present in drivers’

systems. A 2004–2005 survey of labs in the United States conducted by 

SOFT, in conjunction with the National Safety Council and the American 

Academy of Forensic Sciences, shows that the most common drug 

encountered in DUID cases is cannabis (marijuana), followed by 

benzodiazepines (anti-anxiety medications with sedative properties), then 

narcotics (including cocaine, hydrocodone, and morphine/codeine).22

NHTSA and states collect information on drug involvement in fatal 

crashes, but these data are not complete or consistent, according to 

NHTSA officials. States collect data on drug involvement in fatal crashes 

as determined through drug testing of involved drivers, data that then may 

be reported to NHTSA and aggregated in NHTSA’s Fatality Analysis 

Reporting System (FARS).

The 

most common drugs, and how drugs are categorized, differ from region to 

region, as indicated by toxicological results we gathered from seven state 

toxicology labs. Four of the selected states do not separate out DUID 

toxicological testing from other toxicological testing. For the three 

selected states that have separate toxicology data for DUID cases, the 

most common drug found for the most recent data available was 

marijuana; the second most common drug or drug category found was 

methamphetamine for two states and benzodiazepines in one state.

23

 21For instance, under the Drug Free Workplace Program (established in accordance with 

Exec. Order No. 12564, 51 Fed. Reg. 32889 (Sept. 15,1986) a supplemental 

appropriations act for fiscal year 1987, Pub. L. No. 100 -71, 191 Stat. 468 (1987) and the 

Mandatory Guidelines for Federal Workplace Drug Testing Programs, 73 Fed. Reg. 71858 

(Nov. 25, 2008)), the SAMHSA National Laboratory Certification Program establishes 

standards for federal workplace drug testing. The National Commission on Forensic 

Science, a partnership between the Department of Justice and the Department of 

Commerce’s National Institute of Standards and Technology, is currently working to 

develop guidance regarding universal accreditation for forensic-science service providers.

However, according to NHTSA officials, 

comparing FARS results from one state to another is problematic 

22Laurel J. Farrell, Sarah Kerrigan, and Barry K. Logan, “Recommendations for 

Toxicological Investigation of Drug Impaired Driving,” Journal of Forensic Sciences, vol. 

52 no. 5 (2007).

23FARS is a nationwide census providing NHTSA, Congress, and the American public 

yearly data regarding fatal injuries suffered in motor vehicle traffic crashes.

Federal and State Crash 

Data
Page 15 GAO-15-293 Drug–Impaired Driving

because of the limitations and variations in data collection, testing, and 

reporting noted above, among other things.

In addition to limited data on the extent of drugged and drug-impaired 

driving, federal and state officials we spoke with cited difficulty in defining 

drug impairment as a significant challenge to addressing drug-impaired 

driving. Compared to alcohol, which is chemically simple and has 

relatively predictable effects, defining and identifying impairment due to 

drugs is much more complicated due to the large number of available 

drugs and their unpredictable side effects. The lack of a definition of drug 

impairment, in turn, exacerbates challenges in enforcing drug-impaired 

driving laws and informing the public about the dangers of driving under 

the influence of drugs.

Toxicologists in three of seven selected states, officials from NIDA, 

SAMSHA, and representatives from SOFT stated that identifying a link 

between impairment and drug concentrations in the body, similar to the 

0.08 BAC threshold established for alcohol, is complex and, according to 

officials from SOFT, possibly infeasible. Alcohol is a chemically simple 

molecule that is absorbed and metabolized at a relatively consistent and 

predictable rate. In contrast, most drugs are chemically complex 

molecules; various drugs are absorbed and eliminated from an 

individual’s system at different rates. As a result, impairment does not 

necessarily correspond to a specific concentration level in the blood, and 

detectable amounts of certain drugs may remain even after impairing 

effects wear off. For example, as noted earlier, marijuana can be detected 

in a daily marijuana user’s system up to 30 days after using the drug. 

Toxicologists in four states and representatives from SOFT stated that, as 

a result, a positive drug test does not necessarily indicate impairment.

Additionally, drugs can have varying and unpredictable effects on 

individuals. For example, individuals with prescriptions for central nervous 

system depressants, such as a prescription sleep aid, can develop a 

tolerance which can reduce some of the impairing effects. During the first 

few days of taking a prescribed central-nervous-system depressant, a 

person can feel sleepy and uncoordinated, but as the body becomes 

accustomed to the effects of the drug and tolerance develops, these side 

Difficulty of Defining 

Drug Impairment 

Exacerbates 

Challenges Related 

to Enforcement and 

Public Awareness

Defining Drug Impairment 

Is Complex

No Clear Link between Drug 

Concentration and Impairment
Page 16 GAO-15-293 Drug–Impaired Driving

effects begin to disappear. As a result, drug concentrations that would be 

impairing for one individual may not be impairing to another. Further, 

drivers may combine more than one drug or mix drugs with alcohol, which 

can have unpredictable results and cause impairment more quickly than 

the same amounts of each substance taken alone. According to literature 

we reviewed, when combined, multiple drugs or drugs and alcohol can 

have a synergistic effect, rather than a simple additive effect, so each 

substance may increase the impairing effects of the others.

Drug testing is more time consuming and expensive than testing for 

alcohol because rather than the single blood or breath test needed to 

determine blood alcohol level, separate tests must be conducted for each 

suspected drug class (e.g., pain relievers, antidepressants), and the 

required instrumentation is sophisticated and costly.24 According to 

toxicologists from two states and representatives from SOFT, it is more 

expensive to test for drugs than alcohol. For instance, one toxicologist 

stated that standard equipment for alcohol analysis costs between 

$100,000 and $120,000; but equipment needed to test for certain types of 

drugs can cost up to $500,000. Additionally, the number of potentially 

impairing legal and illegal drugs is large. For example, the NRS tested 

drivers for 75 illegal, prescription, and OTC drugs identified as potentially 

impairing, and while some medications do not affect or can even improve 

driving ability, the FDA has identified eight common classes of 

prescription and OTC medications as potentially impairing.25 In addition, 

in 2013, the National Safety Council’s Alcohol, Drugs and Impairment 

Division reviewed and recommended a list of 33 drugs that should be 

included in the scope of drug testing.26

 24Blood and breath tests are two different methods for measuring an individual’s blood 

alcohol level.

25FDA, Some Medications and Driving Don’t Mix, updated October 14, 2014. 

http://www.fda.gov/ForConsumers/ConsumerUpdates/ucm107894.htm. 

26B.K. Logan, K. J Lowrie, J. L. Turri, J. K. Yeakel, J. F. Limoges, A. K. Miles, C. E. 

Scarneo, S. Kerrigan, and L. J. Farrell, “Recommendations for Toxicological Investigation 

of Drug-Impaired Driving and Motor Vehicle Fatalities,” Journal of Analytical Toxicology, 

vol. 37 (2013). 

Analyzing Samples for the 

Large Number of Available 

Legal and Illegal Drugs Is Time

Consuming and Expensive
Page 17 GAO-15-293 Drug–Impaired Driving

Further, new drugs are continually being developed for both legal and 

illegal markets, especially synthetics.27 For instance, the United Nations 

Office on Drugs and Crime reported that in the United States, 51 synthetic 

cannabinoids (developed to reproduce the effects of THC/marijuana) and 

31 synthetic cathinones (mimicking the effects of amphetamines) were 

identified in 2012.28 According to toxicologists in two states, to pursue 

detection of new drugs, even if the molecular structure is only slightly 

different from other known drugs, labs need to develop a new testing 

methodology and then validate that methodology through extensive 

testing on each individual instrument. For example, according to one 

toxicologist, developing and validating testing methods for a new drug 

recently cost about $31,000. Validation of new methodologies is a 

complicated task and requires qualified personnel, time, and money. 

Additionally, one toxicologist stated that, to run tests on synthetic 

cannabinoids and other synthetics, a standard sample against which to 

test must be purchased from either a chemical company or another 

source. The entire process is lengthy and expensive.

State prosecutors and highway safety office officials in three of the seven 

selected states said that there is a lack of knowledge among law 

enforcement about drug impairment in drivers. Furthermore, according to 

officials from NHTSA, GHSA, and IACP, basic training for officers on 

impaired driving enforcement is insufficient for identifying drivers that may 

be impaired by drugs. For example, officers may be trained to administer 

the Standardized Field Sobriety Test, which focuses on detecting alcoholimpairment in drivers; however, officers may not be trained to recognize 

drug impairment. One prosecutor stated that there is a misperception 

among some officers who have not received training to identify drug 

impairment that a drug-impaired driver should exhibit similar symptoms as 

 27Synthetic drugs are chemically produced in a laboratory and may be developed to 

circumvent current drug laws and testing. The chemical structure for synthetics can be 

either identical to or different from naturally occurring drugs, and their effects may be 

designed to mimic or even increase the effects of natural drugs.

28United Nations Office on Drugs and Crime. World Drug Report 2013 (May 2013).

Enforcement of DrugImpaired-Driving Laws Is 

Challenging

Lack of Knowledge among Law 

Enforcement about Drug 

Impairment in Drivers
Page 18 GAO-15-293 Drug–Impaired Driving

a drunken one; including slurred speech and difficulty maintaining 

balance. As a result, officers who are not trained to detect drug 

impairment may mistakenly think that a driver is not impaired. See table 3 

for a comparison of some of the possible symptoms of alcohol and drug 

impairment, which vary depending on the type of drug used.

Table 3: Comparison of Examples of Possible Alcohol and Drug-Impairment Symptoms

Alcohol impairment Depressant impairment Cocaine impairment Marijuana impairment

• slurred speech

• problems with 

balance

• odor of alcohol on 

breath

• slurred speech

• poor performance on field 

sobriety tests

• drowsiness

• disorientation

• drunken behavior without 

the odor of alcohol

• excessive activity

• increased alertness

• talkativeness

• irritability

• argumentativeness

• nervousness

• body tremors

• anxiety

• redness in nasal area and runny 

nose

• poor performance on field 

sobriety tests

• odor of marijuana in car or 

on breath

• bloodshot eyes

• body and eyelid tremors

• incomplete thought 

processes

Source: National Highway Traffic Safety Administration. | GAO-15-293

Note: This table provides examples of drug impairment symptoms, but does not represent the 

universe of possible symptoms. Symptoms of drug impairment vary depending on the type of drug 

used.

The time between arrest and collection of a sample for drug testing can 

affect the quality of biological evidence, such as blood samples, because 

the concentration of drugs in the body is constantly changing. Specifically, 

logistical challenges and legal requirements pertaining to evidence 

collection can increase the time between arrest and sample collection, 

reducing evidence quality. Currently, there is no validated roadside drugtesting device, such as the evidential breath-testing device for alcohol, 

which would facilitate faster sample collection.29

 29While some oral fluid and breath testing devices have been developed to detect drug 

use, they have not yet been validated for use in the field.

Drug testing can be 

conducted from a blood, oral fluid, or urine sample. According to 

toxicologists from two states, representatives from SOFT, and literature 

we reviewed, blood sample analysis is currently the most accurate 

method of detecting recent drug use. Officials in two of the states that we 

selected said that it can be time consuming to obtain a search warrant for 

a blood sample, because it requires approval by a judge. For example, 

Processes for Obtaining 

Samples for Drug Testing Can 

Be Time Consuming and 

Result in Loss of Evidence
Page 19 GAO-15-293 Drug–Impaired Driving

officials from a state highway-safety office stated that a DUID arrest can 

take 3 to 4 hours if blood is being collected, because arresting officers 

must wait for a warrant signed by a judge to conduct the blood test. 

Moreover, depending on local requirements and resources, potential 

offenders may need to be transported by law enforcement to a hospital or 

other location for a phlebotomist or nurse to collect a blood sample, 

leading to further delays.30

According to toxicologists in four states, the lack of qualified lab personnel 

and testing equipment can contribute to a backlog of samples that need 

to be tested for drugs, which can result in long waits for toxicology results. 

In five of the states that we selected, officials told us that current lab 

backlogs ranged from no backlog to about 2,000 cases (the oldest case 

being 2 years old). As a result of a lab backlog, officials in two of the 

states that we selected said that a prosecutor may have to move forward 

with a drug-impaired driving case without toxicology results due to legal 

time constraints for prosecution. Additionally, toxicologists from two states 

said that some drug compounds continue to degrade once blood samples 

have been collected and may not be detectable in the sample three to six 

months after collection, making the evidence less useful or of no use to 

prosecutors.

As the arresting officer waits to collect the 

sample, the drug content in the suspect’s blood can decrease 

significantly, resulting in a less accurate measure of the drug content in 

the blood at the time of the actual traffic stop.

State prosecutors, toxicologists, law enforcement and highway-safety 

office officials from all of the selected states, as well as NIDA, told us that 

they believe that there is a lack of public awareness about the dangers of 

driving after using prescription medications and marijuana. According to 

prosecutors whom we spoke to in three states, alcohol-impaired driving is 

easy for people to understand, because the public has been educated 

about the dangers of drunk driving through various campaigns. However, 

they noted that people believe there is less danger associated with 

prescription medications and, in some cases, marijuana. As a result, 

jurors may have a more difficult time understanding the dangers 

associated with driving under the influence of prescription medication, for 

 30A phlebotomist is an individual trained to draw blood for tests, transfusions, research, or 

blood donations.

Lab Backlogs Can Lead to 

Difficulties in Enforcement and 

Prosecution

Public Awareness about 

Dangers of Drugged 

Driving Is Limited
Page 20 GAO-15-293 Drug–Impaired Driving

example, based on their personal experience of taking similar 

medications without perceiving they are impaired or having a driving 

incident. Additionally, according to state prosecutors, toxicologists and

law-enforcement and highway-safety office officials from all of the 

selected states as well as NIDA, the public perceives that driving after 

using marijuana is not dangerous. Moreover, officials from two state 

highway safety offices and NIDA stated that in their view, the public is 

generally unaware of the unpredictable effects of combining multiple 

drugs. As a result of this perceived lack of awareness, members of the 

public may risk unknowingly driving while impaired, potentially leading to 

vehicle collisions, injuries, and fatalities.

Officials in four states said that there is a lack of focus on drug 

impairment in highway-safety public-education campaigns. For example, 

the traffic-safety-marketing communications resources available on 

NHTSA’s website for states, partner organizations, and highway safety 

professionals who are related to impaired driving are generally focused 

on reducing drunk driving: “Drive Sober or Get Pulled Over” and “Buzzed 

Driving is Drunk Driving.” See figure 1. Additionally, campaigns in the 

states we selected generally use language that may suggest a focus on 

impairment due to alcohol, rather than drugs, for example, “Drive 

Hammered, Get Nailed.”

Figure 1: NHTSA’s “Drive Sober or Get Pulled Over” and “Buzzed Driving is Drunk 

Driving” Campaigns
Page 21 GAO-15-293 Drug–Impaired Driving

Federal and selected state agencies are taking actions to address drugimpaired driving, including the challenges previously cited. These actions 

include improvements in the areas of research and data, education of law 

enforcement and court personnel, evidence quality, legal remedies, and 

public awareness. Furthermore, NHTSA, ONDCP, and states have 

coordinated their efforts to address drug-impaired driving challenges. 

However, NHTSA’s current public awareness initiatives do not clearly 

include drug-impaired driving and state officials we spoke with stated that 

NHTSA could do more to increase public awareness about the dangers of 

drugged driving.

Research on Drug Impairment: Federal agencies have completed and are 

conducting research to increase knowledge about the relationship 

between drugs, impairment, and crash risk. For example, NHTSA is 

currently researching the crash risk of drug and alcohol use (including 

illegal, prescription, and OTC drugs) by collecting samples from more 

than 10,000 crash- and non crash-involved drivers in one city for 20 

months. The results of this study are expected in 2015. Additionally, 

components of HHS, including NIDA, have researched the impairing 

effects of various drugs, including the effects of habitual marijuana use. 

For example, NIDA has conducted research on the length of time 

marijuana can be detected in blood after use (up to about 30 days in daily 

users). Regarding prescription and OTC drugs, the FDA uses information 

from studies conducted by drug manufacturers to assess new 

medications for adverse effects, including drowsiness, and requires that 

those effects are appropriately discussed in labeling, including package 

inserts.31

Data Availability, Consistency, and Timeliness: To increase the 

availability of data on drug-impaired driving, NHTSA has recommended 

that states distinguish among alcohol or drugs, or both for impaired 

driving cases. Some states, including Colorado and Arizona, are 

implementing systems to track whether impaired-driving arrests involved 

 31According to HHS, although the carton or container of a prescription drug supplied by 

the manufacturer may include information concerning adverse effects, such as 

drowsiness, state boards of pharmacies regulate the label of the repackaged container 

that is dispensed to patients.

Federal and State 

Agencies Are Working 

to Address DrugImpaired Driving, but 

NHTSA’s Efforts to 

Improve Public 

Awareness Have 

Been Limited

Research and Data on 

Drug-Impaired Driving
Page 22 GAO-15-293 Drug–Impaired Driving

drugs or alcohol, or both. NHTSA officials stated that such state efforts 

may also help improve federal data sources, such as FARS. Additionally, 

California, Hawaii, and New York have separated driving under the 

influence of alcohol, drugs, or the combined influence of drugs and 

alcohol in their impaired driving statutes, a move that may result in more 

detailed data on the extent of drug-impaired and alcohol-impaired driving.

In 2013, the National Safety Council’s Alcohol, Drugs and Impairment 

Division reviewed and updated a set of minimum recommendations to 

toxicologists for drug testing in suspected impaired-driving cases and fatal 

crashes, including recommendations to improve the consistency of data 

on the frequency with which specific drugs are linked with impaired 

driving.32

Further, some states have initiated or implemented plans to increase the 

capability of toxicology labs to improve the timeliness and availability of 

data. For example, Kansas has made recent efforts to increase the 

capacity of its forensic lab, housed in the Kansas Bureau of Investigation, 

through increased funding to retain specialized technicians, increased 

toxicology staffing, and building a new facility. According to an official 

from the lab, the improvements should help the state decrease its backlog 

of 2,000 toxicology cases (as of August 2014). Additionally, according to 

a lab official, the Ohio Crime Lab received federal grant funding in 2013 to 

purchase needed instrumentation and coordinates with the Indiana 

Specifically, the recommendations included standards for the 

type of sample tested (blood, oral fluid, or urine), the scope of drugs for 

which to test, and cutoff values for reporting the presence of a drug. The 

NTSB has recommended that NHTSA develop and disseminate similar 

standards to state officials. According to NHTSA officials, they have 

discussed these types of standards with officials from SAMHSA, NTSB, 

and ONDCP. SAMHSA has recently developed oral fluid drug-testing 

standards for federal workplaces. These standards are currently under 

review and have not yet been released for public comment. NHTSA 

officials stated that they plan to wait until these workplace standards are 

further along in the approval process in order to develop guidance for 

states that are generally consistent with SAMHSA’s workplace standards.

 32The National Safety Council is a nonprofit advocacy organization focused on preventing 

injuries and fatalities through research, education, and advocacy. B.K. Logan, K. J Lowrie, 

J. L. Turri, J. K. Yeakel, J. F. Limoges, A. K. Miles, C. E. Scarneo, S. Kerrigan, and L. J. 

Farrell, “Recommendations for Toxicological Investigation of Drug-Impaired Driving and 

Motor Vehicle Fatalities,” Journal of Analytical Toxicology, vol. 37, no. 8 (2013).
Page 23 GAO-15-293 Drug–Impaired Driving

Department of Toxicology and the Kentucky State Police Toxicology 

Laboratories to share information and validation techniques for new drugtesting methodologies.

Drug Recognition Expert Program: One strategy for increasing knowledge 

about drug impairment among law enforcement mentioned by officials in

all seven selected states is the Drug Recognition Expert (DRE) program, 

which provides training to law enforcement officers and others to identify 

drivers under the influence of drugs. For this program, IACP and NHTSA 

coordinated to leverage training originally developed in California.33

According to IACP’s 2013 annual report on the DRE program, as of 

December 2013, about 6,750 DREs have been certified in all 50 states 

and the District of Columbia.

The 

training includes 72 hours of classroom training and between 40 and 60 

hours of field training. Law enforcement officers who complete this 

training are certified by states as Drug Recognition Experts (DRE) and 

qualified to perform a 12-step evaluation protocol to assess subjects for 

drug impairment, which includes psychophysical tests and physical 

examinations.

34

• Training is time-consuming and expensive: Beyond the cost for 

training, which is often covered through state and federal grants, 

departments may need to pay for travel and lodging costs as well as 

overtime pay and additional coverage while officers attend training.

While officials in all of the selected states 

said that the DRE program was effective, some also discussed 

challenges related to the program, including:

• Retention of certified officers: Officials from three selected states as 

well as IACP told us that high attrition among DREs makes it difficult 

to maintain enough certified officers. Reasons cited for this attrition 

include:

o DRE-certified officers tend to be high-performing officers and are 

quickly promoted out of traffic units.

 33DREs are trained through the Drug Evaluation and Classification Program, coordinated 

by the IACP with support from NHTSA. 

34International Association of Chiefs of Police, The 2013 Annual Report of the IACP Drug 

Recognition Section (Alexandria, VA: Oct. 20, 2014).

Education for Law 

Enforcement Officers and 

Legal Professionals
Page 24 GAO-15-293 Drug–Impaired Driving

o DRE re-certification requirements are time-consuming and 

expensive and may be difficult for small departments to fulfill.

• NHTSA’s database of DRE reports is difficult to use: NHTSA 

maintains a database of DRE reports (submitted voluntarily by DRE 

officers) as a source of data on the program and drug-impaired 

driving. However, according to law enforcement officials from four of 

seven selected states, the DRE database is difficult to use, and the 

data are not currently available in a format that allows tracking of 

evaluations conducted by individual officers or departments. For 

example, officers from two states said that they have trouble 

accessing the system. They noted that, as such, some officers do not 

report evaluations, making the database incomplete. According to 

NHTSA officials, they periodically provide system improvements to 

make the database easier and more effective for officers to use; for 

example, they are currently determining what identifying information 

may be added to the system to make tracking easier, without 

compromising privacy or security. Additionally, NHTSA has plans to 

improve the system interface and software.

We were not able to identify any comprehensive study on the 

effectiveness of the program through our literature review, but NHTSA is 

currently conducting a study of a sample of DRE reports to examine the 

predictive validity of each of the components of the DRE evaluation; the 

results are expected in early 2015.

Advanced Roadside Impaired Driving Enforcement Program: In addition 

to the DRE program, law enforcement agencies in all seven of the states 

we selected have implemented Advanced Roadside Impaired Driving 

Enforcement (ARIDE) training, which is meant to bridge the gap between 

the basic training on impaired driving provided in most police academies 

and the more intensive DRE program. The 16-hour ARIDE training 

program, developed through coordination between NHTSA, IACP, and 

the Virginia Association of Chiefs of Police, trains officers to identify and 

assess drivers suspected of being under the influence of drugs. 

Additionally, ONDCP, NHTSA, and IACP have coordinated to create an 

online version of the ARIDE class, which could improve access to drug 

impairment evaluation training to law enforcement agencies with more 

limited resources. However, officials from five of the seven states said 

that they do not allow their officers to take the online version of the ARIDE 

class because, in their view, it is not a good substitute for the classroom 

training. NHTSA is currently conducting an evaluation of the ARIDE 
Page 25 GAO-15-293 Drug–Impaired Driving

program, including a comparison of the original training with the online 

version, with an expected reporting date of early 2016.

Education for legal professionals: To increase the chances of successful 

prosecution of drug-impaired drivers, NHTSA grant funding may be used 

for state and regional level Traffic Safety Resource Prosecutor (TSRP) 

and Judicial Outreach Liaison (JOL) positions to provide training, 

education, and technical assistance to state prosecutors, judges, law 

enforcement officials, and toxicologists. For example, TSRPs in Arizona 

and California train toxicologists on providing effective testimony during 

trials. TSRPs also provide technical support to state and local prosecutors 

both generally and on a case-by-case basis to increase local ability to 

convict impaired drivers.

Guidance: Federal Agencies including NHTSA and DOJ have provided 

states with guidance regarding the enforcement of drug-impaired driving 

laws. For instance, DOJ’s Community Oriented Policing Services 

component issued guidance on drug-impaired driving as part of its 

Problem-Specific Guides series. The guide includes a general description 

of drug-impaired driving and its causes as well as strategies to address 

enforcement challenges (many described above) and considerations for 

implementing the strategies described. Similarly, NHTSA published 

Saturation Patrols and Sobriety Checkpoints Guide: A How-to Guide for 

Planning and Publicizing Impaired Driving Enforcement Efforts, which 

guides state and local law enforcement agencies in planning and 

conducting high visibility enforcement campaigns (discussed below).

To improve the likelihood that drug testing results will accurately reflect 

drug concentrations at the time of a traffic stop or crash, some states 

have taken actions to reduce the time between initial contact with law 

enforcement and collection of evidence.

• Roadside testing: Development of an accurate roadside drug-testing 

device, comparable to breath sensors for alcohol detection could 

increase law enforcement officers’ ability to identify drivers who have 

used drugs. Oral-fluid testing devices that are currently available test 

for a limited scope of drugs; representatives from SOFT stated that 

the scope includes the most common drugs found in drivers. NIH has 

conducted studies to validate the results of oral fluid and breath 

testing devices for certain drugs in controlled settings. Further, 

NHTSA is currently conducting research on the feasibility of 

incorporating available roadside oral fluid-testing devices in criminal 

justice processes, with results expected by early 2016. Additionally, a 

Actions to Preserve 

Evidence Quality
Page 26 GAO-15-293 Drug–Impaired Driving

pilot program using various roadside oral fluid-testing devices has 

been conducted in Miami, with varying results depending on the 

device and type of drug. For example, one device was more accurate 

than the other overall, and accuracy for certain drugs was higher than 

for others.

• Electronic warrant systems: Washington and Arizona have 

established or are in the process of establishing electronic warrant 

systems, through which applications for warrants to collect biological 

samples are submitted, reviewed, and either granted or denied via 

electronic means (telephone, fax, or e-mail). According to law 

enforcement officials in those states, these systems can decrease the 

time between arrest and collection of samples for drug testing, in an 

effort to preserve evidence quality

• Increased access to phlebotomy services: For the past 8 to 9

years, Arizona has been training law enforcement officers as 

phlebotomists to reduce the time between arrest and collection of 

samples for drug testing, thus preserving evidence quality.

Sentencing policies: Officials from state agencies in four of seven states 

said that sentencing strategies such as the use of impaired-driving courts 

reduce recidivism through programs that use a model of post-conviction 

supervision and treatment, combined with punishment such as fines, in 

order to change behavior. We have previously reported that participants 

that received such additional supervision and treatment through adult 

drug courts, including designated impaired driving courts, were generally 

less likely to be re-arrested than comparison group members drawn from 

the criminal court system.35

Zero-tolerance per se laws: ONDCP, GHSA, and others have 

recommended that states establish “zero tolerance” laws, which make it 

illegal per se (in itself) to drive with a detectable amount of a prohibited 

drug (defined by state law) in one’s system, regardless of whether there is 

evidence of impairment. According to a 2010 NHTSA report on the 

effectiveness of such laws, the compelling argument for zero tolerance 

laws is that, in their absence, a driver under the influence of an illegal 

 35GAO, Adult Drug Courts: Studies Show Courts Reduce Recidivism, but DOJ Could 

Enhance Future Performance Measure Revision Efforts, GAO-12-53 (Washington, D.C.: 

Dec. 9, 2011).

Legal Remedies
Page 27 GAO-15-293 Drug–Impaired Driving

substance was less likely to be prosecuted for impaired driving than a 

driver under the influence of alcohol. This problem existed because a 

maximum threshold linked to impairment has been established for 

alcohol, but there is no practical way to establish such a level for drugs. 

This study found some anecdotal support that zero tolerance laws 

increased prosecution rates, but a lack of reliable data prevented NHTSA 

from conclusively determining the effectiveness of such laws. Further, 

officials from NTSB stated there is no evidence that zero tolerance laws 

reduce impaired driving (since a driver need not be impaired to be 

prosecuted under the law). As of December 2014, 15 states have enacted 

laws that prohibit driving with a detectable prohibited substance in the 

driver’s body, without any other evidence of impairment. For example, 

Illinois prohibits drivers from having a detectable amount of any illegal 

substance or other prohibited substances listed in the statute in his or her 

system, which would include certain medications such as hyoscyamine, 

which is used to control symptoms associated with gastrointestinal 

disorders. See figure 2.
Page 28 GAO-15-293 Drug–Impaired Driving

Figure 2: Map of States with Zero-Tolerance Per Se Laws and Per Se Laws Based on Drug Concentration Limits, as of 

December 2014

Notes: This map does not include state laws specifically applicable to individuals under 21. 

This map is based on GAO analysis of state laws as of December 3, 2014.

Per se laws/drug concentration limits: Some officials recommend 

establishing “per se” limits, or thresholds, for certain drugs, similar to the 

0.08 BAC limit established for alcohol. These laws make it illegal per se 

(in itself) for a driver to have a specific amount of a certain drug in his/her 

blood, oral fluid, or urine regardless of detectable impairment. As of 

December 2014, six states have enacted per se laws based on drug 

concentration limits for one or more drugs (see fig. 2). For instance, 
Page 29 GAO-15-293 Drug–Impaired Driving

Washington has established a limit of 5 nanograms of THC per milliliter of 

blood for drivers.36 Colorado has implemented a similar law establishing 5 

nanograms of THC per milliliter of blood as a “permissible inference,”

which, according to a state official, means jurors may infer that the 

defendant was impaired but are not required to do so.37 Additionally, 

Nevada and Ohio have developed per se thresholds for certain controlled 

substances including illegal drugs such as cocaine and heroin as well as 

legal drugs such as amphetamines, which can be used to treat conditions 

such as attention deficit disorder and narcolepsy.38

Per se laws based on drug concentration limits may increase 

prosecutions for drivers who are over the established limits, but the 

effectiveness of these laws is unknown and may have unintended 

consequences. Officials from Colorado, Ohio, and SOFT stated that per 

se limits make prosecution of drivers who are over the limits more likely. 

However, others, including officials from California and Washington, 

stated that it may also make prosecution of drivers who were observed to 

be impaired but whose drug test results were under the established limit 

more difficult: once thresholds are established, drivers and jurors may 

develop the false assumption that driving below the established limit is 

legal, even if there is observable impairment. Some toxicologists, 

including representatives from SOFT, stated that per se laws based on 

thresholds may serve a particular policy goal of increasing prosecutions, 

but that a link between the established thresholds and impairment levels 

cannot be supported scientifically. A representative from SOFT also 

stated that, because illegal drugs generally have no medical purpose,

there is a significant difference between establishing per se threshold 

levels for illegal drugs versus per se threshold levels for prescription and 

OTC medications. According to the representative, setting per se limits for 

prescription and OTC medications may cause problems for those who are 

taking medications as prescribed and may not be impaired.

 36Wash. Rev. Code Ann. § 46.61.502(1)(a)-(b). A nanogram is equal to one billionth of 

one gram.

37Colo. Rev. Stat. Ann. § 42-4-1301(1)(a)-(c).

38Nev. Rev. Stat. Ann. § 484C.120, Ohio Rev. Code § 4511.19.
Page 30 GAO-15-293 Drug–Impaired Driving

Some federal and selected state agencies have implemented drugimpaired driving awareness campaigns to increase public knowledge 

about the dangers of drugged driving. For instance, ONDCP developed 

the Teen Drugged Driving: Parent, Coalition, and Community Group 

Activity Guide, which provides coalitions, prevention groups, and parent 

organizations with facts on the dangers and extent of teen and young 

adult drugged driving, parent and community activities for effective 

prevention, and resources to further assist in prevention activities. At the 

state level, Colorado, Washington, and Ohio have conducted public 

awareness campaigns focused on drug-impaired driving. For example, 

Colorado has aired a series of public service announcements focusing on 

the dangers of driving after using marijuana and emphasizing that driving 

impaired remains illegal, even as marijuana has been legalized at the 

state level.

While NHTSA has also established impaired-driving public awareness 

programs, materials associated with these programs do not explicitly 

include information on the dangers of drug-impaired driving. NHTSA’s 

public awareness programs include high-visibility enforcement campaigns 

such as the “Drive Sober or Get Pulled Over” and “Buzzed Driving is 

Drunk Driving” campaigns (see fig. 1, presented previously), which 

according to NHTSA officials, include drug-impaired driving. For these 

campaigns, NHTSA provides media, such as television and radio 

advertisements, to states to help inform the public about the dangers of 

impaired driving and provides grant funding for state and local police to 

perform highly visible checkpoints and patrols to reinforce the concept 

that impaired drivers are at a high risk of being caught and prosecuted. 

However, using the terms “sober” and “drunk” in the campaign slogans 

may indicate that the campaigns are about the dangers of driving after 

consuming alcohol as opposed to drugs.

NHTSA’s mission is to support state traffic safety efforts. However, 

officials from six of seven selected states as well as representatives from 

GHSA stated that public education more explicitly focused on the dangers 

of drugged driving is needed, particularly on impairment due to 

prescription and OTC medications and marijuana. Officials from some 

states recommended actions such as increased education and 

requirements for medical professionals regarding prescription drug use 

and drug-impaired driving, but also recommended that NHTSA expand 

the current messaging on impairment to include the dangers of marijuana 

and prescription drugs, which are not explicitly addressed through 

NHTSA’s impaired driving advertising campaigns.

Efforts to Increase Public 

Awareness about DUID
Page 31 GAO-15-293 Drug–Impaired Driving

According to NHTSA officials, the current lack of data on impairment 

thresholds and the broad range of drug effects make it more difficult to 

concisely communicate the dangers of drug-impaired driving compared to 

alcohol-impaired driving and has prevented them from including drugs 

more explicitly in current messaging. However, the messaging for current 

alcohol-impaired driving campaigns—such as Drive Sober or Get Pulled 

Over—does not specifically allude to the .08 BAC limit. Increased focus 

on information about the potential dangers of driving after using drugs 

could provide an important reminder to drivers that alcohol is not the only 

substance that may impair driving ability. Adding more explicit messaging 

about drug-impaired driving could be relatively simple, and could 

potentially reduce crashes and associated injuries and fatalities.

NHTSA officials also said they have other plans to improve public 

awareness about the dangers of drug-impaired driving. For example, 

NHTSA officials plan to conduct a recurring survey of driver attitudes and 

behaviors regarding drugged and drug-impaired driving. Data from this 

survey could help NHTSA more fully understand any gaps in public 

awareness about the dangers of drug-impaired driving and develop 

appropriate public awareness campaigns to address those gaps. NHTSA 

officials also plan to provide training for physicians and other medical 

professionals on how to inform patients about the dangers of driving after 

taking some prescription and OTC medications. These efforts to improve 

public awareness are in the initial planning stages and could take several 

years to implement.

To leverage the expertise of various stakeholders to address drugimpaired driving, federal agencies—including NHTSA, ONDCP, HHS, 

NTSB, and states—have coordinated to identify strategies to address 

drug-impaired driving. For instance, ONDCP and NHTSA convened a 

roundtable of drug testing and criminal justice experts to examine new 

drug testing technology in 2012, and have since coordinated to initiate the 

additional research and testing of roadside oral-fluid-testing devices 

previously discussed. Additionally, Colorado and Washington have 

established impaired-driving working groups to develop and implement 

strategies for addressing drug- and alcohol-impaired driving. These 

working groups include state and local law-enforcement, traffic-safety, 

public-health, and motor-vehicle agencies as well as representatives from 

the court system, professional organizations, the marijuana industry, and 

others.

Coordination among 

Federal and State 

Agencies
Page 32 GAO-15-293 Drug–Impaired Driving

The lack of complete and reliable data on the extent and nature of drugimpaired driving presents federal, state, and local agencies with 

challenges to developing and implementing effective countermeasures. 

Ongoing and planned activities by NHTSA, ONDCP, and others are 

intended to increase available information on drug-impaired driving and 

strategies to address the problem, and coordination across the various 

federal, state, and local stakeholders is essential to fully implement any 

strategy. For example, development and validation of a roadside oralfluid-testing device may improve evidence collection processes for local 

and state law enforcement, but continued efforts to standardize lab 

procedures, collect and maintain data, educate law enforcement to 

recognize potential drug impairment, and educate prosecutors are also 

important to realize the benefits of faster evidence collection.

Despite limited data and the challenge of defining impairment, federal and 

state agencies have identified and implemented promising activities—

such as the DRE Program, initiatives to reduce the time to collect and 

analyze evidence, and public awareness—to combat drug-impaired 

driving and associated crashes, fatalities, and injuries. For example, the 

DRE Program and high-visibility enforcement campaigns have already 

been implemented in many jurisdictions. NHTSA and other federal 

agencies have initiated, supported, and continue to improve these 

activities. However, state officials consistently noted that their public 

awareness efforts would benefit from additional support from NHTSA to 

help increase public knowledge of the potential dangers of drug-impaired 

driving, including impairment due to some prescription medications and 

marijuana. While NHTSA’s plans to improve public awareness of drugimpaired driving through a survey on public behaviors and attitudes and 

training for medical professionals are promising, these initiatives will take 

time to implement. Additional efforts, such as general messaging 

reminding the public about the impairing effects of some drugs and the 

dangers of driving after using drugs, could help improve public awareness 

in the near term.

We recommend that the Secretary of Transportation direct the 

Administrator of NHTSA to identify actions—in addition to the agency’s 

currently planned efforts—to support state efforts to increase public 

awareness of the dangers of drug-impaired driving. This effort should be 

undertaken in consultation with ONDCP, HHS, state highway-safety 

offices, and other interested parties as needed.

Conclusions

Recommendation
Page 33 GAO-15-293 Drug–Impaired Driving

We provided a draft of this report to DOT, ONDCP, and HHS for review 

and comment. In written comments (reproduced in appendix II), DOT 

agreed with our findings and recommendation. ONDCP had no 

comments. HHS provided technical comments, which we incorporated as 

appropriate.

We are sending copies of this report to the Secretary of Transportation, 

the Director of the White House’s Office of National Drug Control Policy, 

the Secretary of Health and Human Services, interested congressional 

committees, and other interested parties. The report also is available at 

no charge on GAO’s Web site at http://www.gao.gov.

If you or your staff have any questions concerning this report, please 

contact me at (202) 512-2834 or FlemingS@gao.gov. Contact points for 

our Offices of Congressional Relations and Public Affairs may be found 

on the last page of this report. GAO staff who made key contributions to 

this report are listed in appendix III.

Susan A. Fleming

Director, Physical Infrastructure Issues

Agency Comments
Appendix I: Objectives, Scope, and 

Methodology

Page 34 GAO-15-293 Drug–Impaired Driving

The Senate Report accompanying the Transportation and Housing and 

Urban Development, and Related Agencies Appropriations Bill, 20141

To describe what is known about the extent of drug-impaired driving in 

the United States, to identify challenges to addressing drug-impaired 

driving, and to identify actions federal and state agencies have taken to 

mitigate those challenges, we conducted a literature search to identify 

sources of data on the extent of drugged and drug-impaired driving in the 

United States and studies on the issue of drug-impaired driving, including 

challenges and strategies for addressing the problem. We identified 

existing studies from peer-reviewed journals, government reports, and 

conference papers based on searches of various databases, such as 

ProQuest and Transportation Research International Documentation. 

Search parameters included international studies, studies across the U.S. 

and in specific states, and research on drug-impaired-driving challenges 

and countermeasures. These parameters resulted in 394 abstracts, which 

we narrowed to 225 by eliminating, for example, studies addressing only 

the extent of drugged or drug-impaired driving in countries other than the 

United States or studies on the broader topic of drug abuse. We further 

divided the literature into studies on the extent of drugged or drugimpaired driving in the United States and studies on drug-impaired driving 

challenges and countermeasures. Studies including data on the extent of 

requires us to conduct a study on the strategies that NHTSA, ONDCP, 

and states have taken to address drug impairment and assess the 

challenges they face in detecting and reducing drug-impaired driving. 

Pursuant to that mandate, we reviewed the actions of relevant federal 

agencies and selected states as well as relevant literature to identify 

actions taken to address drug-impaired driving and associated 

challenges. Specifically, we analyzed (1) what is known about the extent 

of drug-impaired driving in the United States; (2) what challenges, if any, 

exist for federal, state, and local agencies in addressing drug-impaired 

driving; and (3) what actions federal and state agencies have taken to 

address drug-impaired driving and what gaps exist, if any, in the federal 

response to drug-impaired driving. This review defines drug-impaired 

driving as driving while impaired by illegal drugs or prescription and overthe-counter (legal) medications. This review does not include impaired 

driving among commercial motor carriers, for which different laws and 

regulations apply than for members of the general public.

 1

S. Rep. No. 113-45 (2013).

Appendix I: Objectives, Scope, and 

Methodology
Appendix I: Objectives, Scope, and 

Methodology

Page 35 GAO-15-293 Drug–Impaired Driving

drugged or drug-impaired driving in the United States were reviewed to 

identify the source of the data and limitations. We reviewed these studies 

and determined that they were sufficiently reliable for the purposes of this 

report. Studies on countermeasures to address drug-impaired driving and 

challenges were used to provide additional context and information when 

needed. We also reviewed state laws to develop information regarding 

state zero-tolerance per se laws and state per se laws based on drug 

concentration limits.

Additionally, we reviewed documentation, such as research studies and 

plans and agency guidance, and interviewed officials from relevant 

governmental and non-governmental organizations to identify (1) sources 

of data and their limitations, (2) challenges to addressing drug-impaired 

driving, and (3) actions taken by federal and state agencies to address 

drug-impaired driving as well as gaps in the federal response. Federal 

agencies, advocacy organizations, and professional organizations were 

chosen based on having a mission relevant to the issue of drug-impaired 

driving and recommendations from relevant stakeholders. We interviewed 

officials at relevant federal agencies including the National Highway 

Traffic Safety Administration (NHTSA); the White House’s Office of 

National Drug Control Policy (ONDCP); National Transportation Safety 

Board (NTSB); and Department of Health and Human Services’ (HHS) 

components including the Substance Abuse and Mental Health Services 

Administration (SAMHSA), Centers for Disease Control and Prevention 

(CDC), Food and Drug Administration (FDA), and National Institutes of 

Health (NIH).2

 2

Within NIH, the National Institute on Drug Abuse (NIDA) is the primary institute involved 

in this topic. NIDA is one of the 27 institutes and centers within the National Institutes of 

Health.

Additionally, we reviewed documentation obtained from 

and interviewed officials in seven states: Arizona, California, Colorado, 

Kansas, Ohio, Vermont, and Washington. We reviewed documentation 

and interviewed officials at state agencies responsible for highway-safety 

and drug-impairment programs, advocacy organizations, and professional 

organizations based on recommendations from the state highway-safety 

office. For example, we interviewed officials from state highway-safety 

offices, departments of public health and motor vehicles, state lawenforcement agencies, Drug Recognition Expert (DRE) program 

coordinators, state Traffic Safety Resource Prosecutors (TSRP), 

associations of police chiefs and district attorneys, state and local 

toxicologists, and local interest groups. We selected these states based 
Appendix I: Objectives, Scope, and 

Methodology

Page 36 GAO-15-293 Drug–Impaired Driving

on recommendations from federal officials and representatives from 

advocacy and professional organizations and to represent a variety of 

laws, programs, and other factors. Our selection included:

• states with legalized recreational marijuana,

• states that geographically border states in which recreational 

marijuana use has been legalized,

• states with legalized medical marijuana,

• states representing a variety of drug-impaired driving laws, and

• states identified as having robust programs dealing with driving under 

the influence of drugs.

We also reviewed documentation and interviewed representatives from 

advocacy and professional organizations including the Governors 

Highway Safety Association (GHSA), National District Attorneys 

Association, Society of Forensic Toxicologists, Inc. (SOFT), Mothers 

Against Drunk Driving (MADD), International Association of Chiefs of 

Police (IACP), Insurance Institute for Highway Safety, and National 

Council of State Legislatures (NCSL).

We conducted this performance audit from April 2014 through February 

2015 in accordance with generally accepted government auditing 

standards. Those standards require that we plan and perform the audit to 

obtain sufficient, appropriate evidence to provide a reasonable basis for 

our findings and conclusions based on our audit objectives. We believe 

the evidence obtained provides a reasonable basis for our findings and 

conclusions based on our audit objectives.
Appendix II: Comments from the Department 

of Transportation

Page 37 GAO-15-293 Drug–Impaired Driving

Appendix II: Comments from the Department 

of Transportation
Appendix II: Comments from the Department 

of Transportation

Page 38 GAO-15-293 Drug–Impaired Driving
Appendix III: GAO Contact and Staff 

Acknowledgments

Page 39 GAO-15-293 Drug–Impaired Driving

Susan A. Fleming, (202) 512-2834 or FlemingS@gao.gov

In addition to the contact above, Sara Vermillion (Assistant Director), Ria 

Bailey-Galvis, Melissa Bodeau, D. Kyle Fowler, Katie Hamer, Sara Ann 

Moessbauer, Cheryl Peterson, and Maria C. Staunton made key 

contributions to this report.

Appendix III: GAO Contact and Staff 

Acknowledgments

GAO Contact

Acknowledgments

(541115)
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