Driving Impairment and
Crash Risk
Including Drug-Drug and
Drug-Alcohol Interactions
Richard Compton
National Highway Traffic Safety Administration
Addressing Drug-impaired
Driving
• What drugs (other than alcohol) impair
driving
• What drugs people use and drive
• What drugs increase crash risk
• What is the effect of combined use of
alcohol and drugs on driving
• What is the combined effect of multiple
drug use on driving
The Alcohol Model
• Efforts to eliminate the alcohol crash
problem have spanned more than 60
years
• Considerable progress has been made
– In the US:
• 1960’s some 50% of fatal crashes involved alcohol
• Now down to 30%
• With almost 13,000 A/R deaths we have a
long way to go
What it Took to Get Where We
are Today
• Evidence that alcohol impairs driving related
skills
– Laboratory studies
– Simulator studies
– Instrumented vehicle studies
• Evidence about impairment threshold
– Impairment starts with the first drink
– Dose – Response relationship
• Evidence that alcohol raises the risk of crashing
– Case-Control studies to estimate crash risk at various BACs
Alcohol Relative Risk Estimate
180.00
Relative Crash Risk (BAC 0.00 = 1.0)
160.00
140.00
120.00
100.00
80.00
60.00
40.00
20.00
0.00
0.00 0.02 0.04 0.06 0.08 0.10 0.12 0.14 0.16 0.18 0.20 0.22 0.24
BAC Level
Technology to Measure BAC
and Improved Laws
• Technology to measure BAC
– Breathalyzer
• Improved laws
–
–
–
–
–
–
Impairment laws
Presumptive laws
Administrative Per Se laws
Illegal Per Se laws
Lower BAC limits
Minimum Drinking Age – Zero Tolerance laws
What it Took to Get Where We
are Today
• Tools for law enforcement
– SFST
– Portable breath test devices
– LELs
• Education for Prosecutors and Judges
– TSRPs
– Judicial Fellows
What it Took to Get Where We
are Today
• Research on the effectiveness of:
– Laws
– Enforcement techniques
• Sobriety Checkpoints. HVE, Saturation Patrols, DUI
squads
– Sanctions
• Tiered sanctions for multiple offenders
• High BAC Laws
• Ignition Interlocks
– Preventive programs
What Do We Need to Know
About Drug Impaired Driving?
• Evidence that specific drugs impair driving
ability
– Large number of potentially impairing drugs
• Illegal, Prescription, Over-the Counter
• Physiological, behavioral, cognitive
• The research could take decades and cost tens of
millions
– Protocol to Determine Whether a Drug
Impairs Driving Related Skills
Drug Use and Driving
Impairment
• Some drugs have been shown to impair
driving related skills
– Laboratory, simulator, instrument vehicles
(closed course and on-road studies)
• Physiological, behavioral, cognitive
People Drive After Using Drugs
• Drivers use drugs
– Anecdotal
– Expert opinion
– Tests for drug use:
• Arrested drivers
• Injured drivers
• Fatally injured drivers
– DRUID Epidemiological Study
– US 2007 National Roadside Survey
Case Study: Marijuana
• Many studies have looked at marijuana
– Evidence is quite mixed
• Does marijuana impair driving?
– Most studies find impairment, some do not
• Does marijuana increase crash risk?
– Evidence is split
» Reduced risk
» No effect
» Increased risk
The Threshold Issue
• Evidence about dose response relationship
– Impairment thresholds?
– Do higher blood or oral fluid levels mean
greater impairment?
• Probably not going to happen anytime
soon, if ever
Prevalence of Alcohol & Other
Psychoactive Drugs in Drivers in
General Traffic
• DRUID (Driving Under the Influence of
Drugs)
• WP2 – Prevalence of use of alcohol, illicit
drugs and psychoactive drugs by drivers
• Thirteen countries participated in roadside
surveys (BE, CZ, DK, ES, FI, HU, IT, LT,
NL, NO, PL, PT, SE)
DRUID Roadside Surveys
• Nearly 50,000 randomly selected drivers
participated
• Between January 2007 and July 2009
• Drivers of passenger cars and vans
• Stratified multistage sampling design
DRUID Prevalence Study
Methods
• Time of data collection
– Weekdays
4:00 pm – 10:00 pm
– Weeknights:
10:00 pm – 4:00 am
– Weekend days
4:00 pm – 10:00 pm
– Weekend nights 10:00 pm – 4:00 am
• Oral fluid – all countries
– StatSure Saliva Sampler
• Blood – 4 countries (BE, IT, NL, LT)
DRUID Prevalence Study
Results
• On European roads alcohol was the most
prevalent drug, followed by illicit drugs
and medicinal drugs
– Alcohol
3.48%
– Illicit drugs 1.36%
– Medicines 0.37%
• Considerable variation between countries
in drug use rates
Most Commonly Detected
Substances
•
•
•
•
•
•
•
Alcohol
THC
Benzodiazepines
Cocaine
Medicinal opiates
Amphetamines
Illegal opiates
3.48%
1.32%
0.90%
0.42%
0.35%
0.08%
0.07%
Drug and Alcohol Combinations
• Alcohol and other drugs
0.37%
• Multiple drugs
0.39%
2007 National Roadside Survey
(NRS) of Alcohol and Drug Use
In a nationally representative sample of
drivers in the United States:
• Determine the incidence of drivers at
various BACs
• Determine the incidence of drugs in the
oral fluid and blood of drivers (illegal,
prescription, & over the counter)
Background
• 3 previous National Roadside Surveys (conducted
Friday and Saturday evenings)
– 1973 (NHTSA)
– 1986 (IIHS)
– 1996 (NHTSA-IIHS)
• Decreasing trend in alcohol-positive drivers
– 1973 – 36%
– 1986 – 26%
– 1996 – 17%
Design
• For comparability with previous roadside
surveys of alcohol use by drivers data was
collected weekend nights
– Primary alcohol-related crash problem
• Unknown whether drug use by drivers
differs between day and night, weekday and
weekend so weekday daytime included
– Recreational use of drugs might parallel alcohol use
Study Sites
National Automotive Sampling System (NASS)
– General Estimates System (GES)
• Carefully selected set of sites
designed to yield a nationally
representative sample of crashes
• 60 locations across the US (PSUs)
• 5 sites randomly selected in each PSU
NASS-GES
Primary Sampling Units (PSUs)
WA
WI
MA
NY
MI
PA
IA
NE
IL
OH
IN
CO
CA
NJ
MD
VA
MO
KY
TN
AZ
NC
OK
NM
AL
TX
FL
National Automotive Sampling System - General Estimates System (NASS-GES)
Data Collection Days & Times
• Weekends
– Friday night
– Saturday
– Saturday
– Sunday
10:00 pm – 12:00 am
1:00 am – 3:00 am
10:00 pm – 12:00 am
1:00 am – 3:00 am
• Weekday
– Friday
– Friday
9:30 am – 11:30 am
1:30 pm – 3:30 pm
Percentage Weekend Nighttime
Drivers Positive for Alcohol
Percentage of Drivers
40
36.1
35
30
25.9
25
16.9
20
12.4
15
10
5
0
1973
1986
1996
Year
2007
Overall Prevalence Rates for
Alcohol and Drugs
• 16.3% of weekend nighttime drivers
positive for drugs
• 14.3% of weekend nighttime drivers
positive for illegal drugs
• 12.4% of weekend nighttime drivers
positive for alcohol
Alcohol Prevalence by
Time of Day
N
Time of Day
(Unweighted)
% Alcohol Positive
(Weighted)
Daytime
2,466
1.0%
Nighttime
8,189
12.4%
Drug Prevalence by
Time of Day
(Oral Fluids)
N
Time of Day
(Unweighted)
% Drug Positive
(Weighted)
Daytime
1,850
11.0%
Nighttime
5,869
14.4%
Drug Prevalence by Time of Day
and Session (Oral Fluids)
N
(Unweighted)
% Drug Positive
(Weighted)
Friday Daytime
(9:30 - 11:30 am)
(1:30 – 3:30 pm)
1,850
11.0%
Friday Nighttime
(10:00 -12:00 pm)
1,610
12.9%
Saturday Early Morning
(1:00 – 3:00 am)
1,299
17.2%
Saturday Nighttime
(10:00 -12:00 pm)
1,684
13.6%
Sunday Early Morning
(1:00 – 3:00 am)
1,276
17.4%
Session
Drug Prevalence by Vehicle
Type (Oral Fluid and Blood)
Vehicle Type
Passenger Vehicle
N
(Unweighted)
% Drug Positive
(Weighted)
1,944
18.0%
Pickup
393
10.7%
SUV
583
12.9%
Van & Minivan
250
19.6%
46
35.4%
3,216
16.8%
Motorcycle
Overall
Drug Categories
(Oral Fluid and Blood)
Drug Category
N
(Unweighted)
%
(Weighted)
Illegal
313
10.8%
Medications
201
4.9%
45
1.1%
Negative
2,676
83.2%
Overall
3,235
100.0%
Illegal & Medications
“Medications” includes prescription and over-the-counter drugs. In this table, percentages are weighted.
BAC by Drug Prevalence
(Oral Fluid and Blood)
BAC (g/dL)
Drug
Result
N
(Unweight
ed)
Positive
Zero
Between
Zero and .08
.08+
559
80.6%
14.0%
5.3%
Negative
2,676
93.9%
5.1%
1.0%
Overall
3,235
91.7%
6.6%
1.7%
In this table, percentages are weighted.
Percent BAC Positive by Time of
Day and Drug Use (Oral Fluid)
[Percent Drug Positive Who were Alcohol Positive or Negative]
BAC
Time of Day
Daytime
Nighttime
Drug
Positive
Negative
Positive
1.8%
(4)
Negative
0.8%
Overall Daytime
0.9%
98.2%
(N)
(242)
246
(13)
99.2% (1,586)
1,599
(17)
99.1% (1,828)
1,845
Positive
19.5%
(163)
80.5%
(673)
836
Negative
9.8%
(163)
90.2% (4,538)
5,031
11.2%
(656)
88.8% (5,211)
5,867
Overall Nighttime
Number of Drug Classes (Blood)
Number of
Drug Classes
1
N
%
(Unweighted)
(Weighted)
398
11.8%
68
2.0%
Negative
2,810
86.2%
Overall
3,276
100.0%
2+
Fatality Analysis Reporting
System (FARS)
• Drug use prevalent among fatally injured
drivers
– Fatally-injured drivers: 33% (2007)
• Drug testing in FARS is inconsistent
– 12 States at or above 80%
– 15 States at or below 40%
– Some States report drug test results for few
fatally injured drivers
DRUID Estimated Relative Risk
of Injury/Death of Driving While
Positive for Psychoactive Drugs
• Nine EU countries participated
– Six countries looked at the relative risk of
getting seriously injured
• DE, FI, LT, IT, BE, NL
– Four countries looked at the relative risk of
getting killed
• FI, NO, SE, PT
Case Control Study
• Use of psychoactive substances was
compared between drivers who were
seriously injured or killed in crashes with a
random sample of drivers taken from the
DRUID roadside survey
Study Population
• Crash involved seriously injured or killed driver
samples came from hospital studies of seriously
injured and killed drivers
– 2,490 seriously injured drivers
– 1,112 killed drivers
• Control drivers came from the roadside surveys
in the same countries
– 15,832 control drivers for the seriously injured sample
– 21,917 control drivers for the killed drivers
Calculation of Relative Risk
• Data weighted by time period for the
control drivers
• Adjusted for age and gender
• Odds ratios calculated separately for each
country
• Aggregated odds ratios based on all
countries or a subset of countries
Results
• Considerable variation between countries
in relative risks/odds ratios
• Confidence limits quite wide
• Non-response rates in control samples
were sometimes quite large
High Risk Drugs
• Highest risk (20-200 times the risk of a
sober driver) of getting seriously injured
or killed associated with:
– High alcohol concentrations (above 1.2 g/L)
– Alcohol combined with other psychoactive
substances
Other High Risk Groups
• High risk (5-30 times the risk of a sober
driver) of getting seriously injured or killed
associated with:
– BACs between 0.8 g/dL and 1.2 g/L
– Multiple drug use
– Amphetamines
Medium Risk
• Medium risk (2-10 times the risk of a
sober driver) of getting seriously injured
or killed associated with:
– Alcohol concentrations between 0.5 g/L and
0.8 g/L
– Cocaine
– Benzoylecgonine
– Illicit opiates
– Medicinal opiates
Lower Risk
• Lower risk (1-3 times the risk of a sober
driver) of getting seriously injured or killed
associated with:
– Low alcohol concentration between 0.1 g/L
and 0.5 g/L
– THC
US Study to Estimate Crash Risk
of Driving While Positive for
Alcohol and Other Drugs
• NHTSA is in the process of completing a
Case-Control study to estimate the crash
risk of driving while impaired by drugs
– 2,500 crash involved drivers
– 5,000 similarly exposed control drivers
Design
• Crash and Control drivers samples
collected at the same location, day of
week, time of day, direction of travel
– Control sample collected one week later
– Two controls for every crash involved driver
• Collect breath test, oral fluid and blood
samples
• Conduct interviews
Design
• Crash Involved Driver Sample
– Go teams respond to reports of crashes
• Police officer and researcher/phlebotomist (Assistant)
–
–
–
–
Seven days a week – 24 hours a day
Weekend nights multiple teams
Passenger vehicle drivers
Excluded:
•
•
•
•
•
Drivers of commercial vehicles
Drivers under 16 years old
Non-English speaking
Extremely impaired drivers
Drivers in emotional distress
Design Continued
• Crash Involved Drivers Included
– Drivers transported to a hospital
– Drivers sent to medical examiner
– Drivers arrested for impaired driving
– Hit and Run drivers (included if apprehended
w/in 2 hours of crash)
• Data Collected in Virginia Beach, VA
• February 2010 – August 2011
Results
• To be released soon!
Multiple Psychoactive Substance
Use
•
•
•
•
Alcohol and drugs
Multiple drugs
More evidence needed
Laws need to address multiple impairing
substance use
– Separate offense
– Enhanced sanctions
Questions?
09/26/11
Technology to Measure the
Presence of Drugs
• Current situation: blood and urine
• Drawing the sample
• Testing the sample
– Screening tests
– Quantitative tests
– Cost and time issues
• What is needed
– Quick (roadside or stationhouse)
– Easy (oral fluids)
– Accurate
• Testing Standards
– Oral Fluid testing standards under development
Improved Laws
• Improved laws
– Zero tolerance for illegal drugs
– Drug impaired drivers are drug impaired
drivers
• Legal prescription may negate illegal possession
charges but not impaired driving
• Alcohol is a legal drug but that does not excuse
alcohol impaired driving
Improved Laws
– Separate statutes for alcohol and other drugs
• Incentive for law enforcement to look beyond
alcohol
– Enhanced sanctions for multiple impairments
• Under existing statutes multiple charges arising
from the same event are prohibited
• Synergistic effects
• Different impairments
Tools for Law Enforcement
• NHTSA and IACP have teemed to offer a
tiered approach to law enforcement
training
• Eight hour drug block
• Advanced Roadside Impaired Driving Enforcement
(ARIDE) – 16 hours, new on-line training coming
soon
• Drug Evaluation and Classification (DEC) program DREs
Training for Prosecutors and Judges
• Training programs developed for
prosecutors
– Joint training with law enforcement
• Training available for judges
– National Judicial College
Education
• Education on the dangers of driving
impaired by drugs
– Physicians
• NHTSA has worked with the AMA to develop
training for physicians on the dangers of
prescription drugs that may impair driving
– Pharmacists
• APA
– Drivers
– FDA
Research on Program
Effectiveness
• Laws
– Per Se (Zero Tolerance)
• Enforcement techniques
– ARIDE
– DEC
• Sanctions
• Prevention programs