Acute Marijuana Intoxication
Contributes to Fatal Motorcycle Accident
This case study illustrates how circumstantial evidence can be misinterpreted and
how drug-impaired judgment and behavior can be regarded as evidential in a toxicological
A motorcyclist was fatally injured when he collided with a city bus in a business
district. The weather was clear and fair, the posted speed limit was 30 mph and
traffic was reported to be light at the time of the collision. The bus (which was
empty and traveling at approximately 25 mph) was making a left turn into
a bus garage terminal when the collision occurred. The driver died on impact.
Witnesses stated that the motorcyclist attempted to decelerate as the bus turned,
but the back tire of the motorcycle rose into the air, causing the bike to flip
over and collide with the bus. A multi-camera DOT video recording from the bus revealed
no apparent events or unusual distractions. Witnesses reported that the motorcycle
was traveling at a high rate of speed (later confirmed through accident reconstruction
analyses to have been approaching 100 mph).
The motorcyclist's family alleged negligence on the part of the bus driver and filed
a lawsuit, demanding not less than $3.8 million dollars. Defense attorneys representing the bus company retained
Dr. Sawyer to conduct an independent toxicological assessment.
Dr. Sawyer compiled and reviewed the case records including accident scene photos,
multiple video recordings from the bus cameras, police reports and diagrams, witness
statements, climate data, the medical examiner's autopsy report, the forensic toxicology
report and the motorcyclist's personal medical records. Upon closer scrutiny, several
significant factors relevant to the case came to light:
- Two weeks prior to the accident, the young motorcyclist had been examined by a doctor after complaining
of dizziness. At that time, he revealed that he had smoked marijuana earlier in the
day. Although there was a history of occasional alcohol consumption noted in his
medical report, marijuana consumption appeared to be a more regular activity.
- Several witnesses reported seeing the motorcycle traveling at high speed
just prior to the accident. Although this could not be immediately corroborated.
closer examination of the video revealed that the motorcycle was
approximately 300 feet away when the bus began to turn. Had the motorcycle been
traveling at 30 mph, it would have taken 7 seconds to cover that distance; instead, it
took less than 3 seconds to reach the turning bus.
- The soundtrack from the video recording revealed that the motorcyclist had downshifted
2 seconds prior to impact rather than initially applying brakes to avoid the collision.
This decision was remarkable given the high rate of speed at which the motorcycle
- The autopsy revealed no alcohol in the motorcyclist's blood. However, active cannabinoid
and its metabolites (the constituents of marijuana) were detected in the postmortem blood analysis.
Based on these findings, Dr. Sawyer elected to conduct a pharmacokinetic assessment
to determine when the marijuana was smoked and if the reported cannabinoid blood
levels were consistent with impairment sufficient to degrade the motorcyclist's
reaction time and judgment at the time of the accident. In toxicology, the metabolite
ratios of THC (delta-9-tetrahydrocannabinol, the psychoactive ingredient in marijuana) can
be measured for this purpose. Dr. Sawyer relied on controlled studies which documented
the ratio of active THC to the carboxy-THC metabolite to determine the time elapsed
since dosing. This, in turn, would establish when it was administered and whether
the blood level was sufficient to contribute to the accident.
The two primary metabolites at issue are the 11-hydroxy (active) and delta-9-carboxy
(inactive) THC metabolites. Initially after smoking, active THC blood levels rapidly
rise with peak levels occurring at approximately five minutes and then decreasing.
Simultaneously, the delta-9-carboxy THC metabolite slowly increases (accumulates)
as THC is transformed into the inactive metabolite. After 10 to 15 minutes, levels
of these two metabolites are approximately equal.
The total and relative amounts of these components were significant
in this case. Since the motorcyclist's postmortem blood analysis revealed slightly more
active THC vs. carboxy-THC levels (2.8 and 2.7 ng/ml, respectively), Dr. Sawyer
was able to offer a supported opinion that the motorcyclist smoked marijuana approximately
10 to 15 minutes before his death.
Additionally, Dr. Sawyer cited a recent peer-reviewed study by Ramaekers, et.
al.1,2 which demonstrated that the blood levels
of delta-9-THC and delta-9-carboxy-THC (marijuana metabolite) are generally
equal at approximately 10 to 15 minutes after smoking. He further cited studies
documenting adverse motor control and cognitive effects, using up to 20 subjects
in a controlled setting. Primary findings included:
- Peak impairment occurred within the first hour after smoking.
- Impairment was significant at THC levels between 2 and 5 ng/ml. For reference,
this level is similar to a blood alcohol concentration (BAC) of 0.08%.
- Cognitive function deficits (based on the "Tower of London" test) and impaired reaction time.
- Impairment was relevant to the safe operation of the motor vehicle.
Dr. Sawyer assembled a detailed report and presented his testimony to the court.
His findings offered objective reasoning (supported by peer-reviewed studies and
substantial toxicological literature) that the motorcyclist displayed impaired judgment
with respect to operating his motorcycle at high speed down a city street. The reaction
of downshifting rather than braking just prior to the crash strongly suggested an
impaired response. Dr. Sawyer further noted that event reconstruction experts estimated
a speed in excess of 100 mph before impact. All of these factors were consistent
with THC impairment based on the blood analysis. As a consequence, the motorcyclist presented
an unreasonable scenario that the bus driver could not have avoided.
Plaintiffs' counsel vehemently denied Dr. Sawyer's findings and filed strongly worded
pre-trial Frye motions to exclude his testimony, accusing Dr. Sawyer of presenting
testimony which "…lacks foundation, is speculative, is based on hearsay
and invades the province of the jury."
Dr. Sawyer addressed these attacks point for point in his rebuttal. In particular,
he noted that plaintiffs' assertion that the level of THC was insufficient to induce
impairment was incorrect. Dr. Sawyer cited numerous sources from NTSB (National
Transportation Safety Board)3,4 and others demonstrating
that the THC dose was more than sufficient to impair judgment, reaction time and
Plaintiffs also asserted that a third THC metabolite (11-hydroxy delta-9 THC) should
have been present at one-fifth the level of delta-9 carboxy THC but was not detected
in the blood analysis. Dr. Sawyer pointed out that the amount in the motorcyclist's
blood was below the laboratory level of detection (LOD). Thus, it did not mean that
the chemical was absent but that it was below the minimum level that the laboratory
instrument could detect. Dr. Sawyer further noted that if the motorcyclist had smoked
the cited quantity of marijuana 10 to 15 minutes before the accident as outlined,
the THC blood levels would have been precisely as measured in the autopsy report.
Expert testimony based on scientific principles or procedures is admissible in court
but only after a principle or procedure has gained general acceptance in its specified
field. All of the sources cited by Dr. Sawyer in his toxicological assessment were
from generally-recognized, peer-reviewed and governmental sources accepted by the
relevant toxicological community.
Dr. Sawyer's assessment left very little "wiggle room." The judge dismissed
plaintiffs' Motion to Exclude without even a written summation. It took the jury
a mere 30 minutes to render a defense verdict of "Not Liable."
At the present time, some states have legalized marijuana and others are leaning
in that direction. As this process unfolds, it will become increasingly
important for both scientific and legal professionals to offer causative determinations
that are both scientifically credible and socially responsible. However, distinguishing
between fact and opinion is not as easy as it may appear. To that end, it is helpful
to remember that the "weighing instrument" for "weighing evidence" is always human
In this case, objective blood levels and metabolite ratios provided the court with
its most compelling scientific evidence. Dr. Sawyer's attorney client kindly characterized
his courtroom testimony as "…truly impressive and the highlight of the
(Disclaimer: Toxicology case studies are impartial and objective summaries of toxicological
matters in which TCAS was retained for the purpose of assessing health-based
factors which, in some cases, led to a determination of causation. No names or identifying
information have been provided due to privacy and legal considerations. In the above
matter, Dr. Sawyer was retained by defendant.)
Notes and References
- Ramaekers, et. al., "Dose related
risk of motor vehicle crashes after cannabis use," 2004 Feb 7;73(2):109-19
- Ramaekers, et. al., "Cognition
and motor control as a function of delta-9-THC concentration in serum and oral fluid," 2006 Nov 8;85(2):114-22
- National Highway Traffic Safety Administration, "Marijuana & Alcohol Combined
Increase Impairment," Number 201, June 1999
- Christopher Hart, National Transportation Safety Board, "Planes, Trains and
Automobiles: Operating While Stoned," Washington, DC July 31, 2014
- Photo by Krzysztof Szkurlatowski
- Photo by Cathy Kaplan, Pittsburgh, PA
- Photo by Matthew Maaskant, Toronto, ON
- Photo by Jason Morrison