Taking alcohol, cannabis, opioids, or other drugs can significantly impact the ability to safely control a vehicle, as well as the ability to notice and respond to hazards in the road.

Our research has focused on understanding

  • How drugs affect driving performance
  • The relationship of drug pharmacokinetics (how drugs are processed in the body) to the changes in driving performance
  • How impairment from drugs that impair driving performance can be detected

Contact

Timothy Brown

Timothy Brown

Title/Position
Research Scientist and Director of Drugged Driving Research

Major findings 2010–2020

Some of our major findings from 2010 to 2020 are described below.

Alcohol

We’ve confirmed that alcohol significantly impacts the ability of drivers to control their vehicle if they have a blood-alcohol concentration of 0.08%1,2 (legal limit) and also at 0.05%3 (as recommended by the National Transportation Safety Board). When looking at urban driving, we found that at 0.05% BAC, drivers tended to drive faster and had a harder time staying centered in their lane. However, they did not exhibit more frequent lane departures similar to what is seen with drivers above 0.08% BAC.3

A research assistant demonstrates how vaporized cannabis is inhaled using heated air in place of cannabis.
A research assistant demonstrates how vaporized cannabis is inhaled using heated air in place of cannabis.

Cannabis

When considering the impacts of cannabis on driving performance, our research has shown that following acute usage of inhaled cannabis, drivers had less vehicle control both laterally4 and longitudinally.5

Even when they were not under the influence of cannabis, regular cannabis users were found to drive differently than non-cannabis users. Young adult drivers who use cannabis—but were sober at the time of our study—drove slower but also steered significantly less often and used the gas pedal less often than drivers who did not use cannabis.6 This suggests that lasting effects of cannabis use persist and may lead to detrimental driving behaviors even after intoxication has subsided. These findings have implications for legislation in support of legalizing cannabis because sober cannabis-using drivers may still be a public health concern.

Other drugs

Our research has also shown that other drugs may negatively impact the ability to control a vehicle, including triazolam, diphenhydramine, alprazolam, and benzodiazepine.2,7-10 Diphenhydramine, for example, caused more variability of lane position as well as increased lane departures, steering bandwidth, average speed, and the percentage of time spent more than 5 mph over the speed limit.9

Pharmacokinetics and measuring impairment

Understanding how drugs are processed in the body and their relationship to impairment is critical to providing appropriate guidance to people using the drugs as well as to policy makers as they consider the legal implications of impaired driving. Impairment from alcohol is more predictable from person to person11 than impairment from cannabis, which has shown more variability in its effects on driving performance.12-14 Blood levels of THC, for example, did not accurately represent observed levels of driving impairment—making it more difficult to predict driving behavior when under the influence of cannabis.15

Knowing that detection of drug impairment can be complicated, there is a dedicated effort to develop methods for determining whether an individual is impaired or just has drugs present in their system. Our research has shown that impaired driving can be detected based on driving data,1,16 vision-based data,17,18 and EEG data.19 Detection of impairment outside the context of driving is also possible as demonstrated by the relationship between EEG based tests and observed driving impairment.20,21 These results show that a simple EEG based test focused on theta activity in the frontal brain area, the area responsible for executive function, could be developed with a limited number so sensors to detect cannabis impairment.

References

  1. Lee J, Brown T, Fiorentino D, Fell J, Traube E, Nadler E. Using Vehicle-Based Sensors of Driver Behavior to Detect Alcohol Impairment. Paper presented at: 22nd International Technical Conference on the Enhanced Safety of Vehicles (ESV); June 13-16, 2011; Washington, DC.
  2. Brown T, Milavetz G, Murry DJ. Alcohol, Drugs and Driving: Implications for Evaluating Driver Impairment. Annals of Advances in Automotive Medicine. 2013;57:23.
  3. Brown TL, Lee JD, Fiorentino D. Effects of Alcohol at 0.05% Blood Alcohol Concentration (BAC) on Low Speed Urban Driving. Traffic Injury Prevention. 2018;19(sup2):S175-S177.
  4. Hartman RL, Brown TL, Milavetz G, et al. Cannabis Effects on Driving Lateral Control with and without Alcohol. Drug and Alcohol Dependence. 2015;154:25-37.
  5. Hartman RL, Brown TL, Milavetz G, et al. Cannabis Effects on Driving Longitudinal Control With and Without Alcohol. Journal of Applied Toxicology. 2016.
  6. Brown T, Banz B, Li K, et al. Variability of Baseline Vehicle Control Among Sober Young Adult Cannabis Users: A Simulator-Based Exploratory Study. Traffic Injury Prevention. 2019.
  7. Milavetz G, Brown T, Murry D, Berka C, Johnson R, Spurgin A. Evaluating Drugged Driving: Further Studies Using a Central Nervous System Stimulant or Depressant. Paper presented at: 58th Annual Scientific Conference of the Association for the Advancement of Automotive Medicine2014; Munich, Germany.
  8. Brown T, Spurgin A, Milavetz G, Gaffney G, Johnson R. Do Drowsy Driver Drugs Differ? 8th International Driving Symposium on Human Factors in Driver Assessment, Training, and Vehicle Design; June 22-25, 2015, 2015; Park City, UT.
  9. Spurgin A, Brown T, Gaspar J, Milavetz G, Gaffney G, Johnson R. Evaluating Drugged Driving: A Comparison of the Pharmacodynamic Effects of Two Central Nervous System Stimulants on Common Driving Performance Measures. American College of Clinical Pharmacy Global Conference on Clinical Pharmacy; October 17–21, 2015, 2015; San Francisco, CA.
  10. Stone B, Correa K, Brown T, Spurgin A, Johnson R. Behavioral and Neurophysiological Signatures Of Benzodiazepine-Related Driving Impairments. Frontiers in Psychology. 2015.
  11. Brown T, Fiorentino D, Lee J, Salisbury S. Variability in Alcohol Absorption: Implications for Studying Alcohol Impaired Driving. 54th Scientific Meeting of the Association for the Advancement of Automotive Medicine; 2010; Las Vegas, NV.
  12. Hartman RL, Anizan S, Jang M, et al. Cannabinoid Disposition in Oral Fluid after Controlled Vaporizer Administration with and without Alcohol. Forensic Toxicology. 2015:1-19.
  13. Hartman RL, Brown TL, Milavetz G, et al. Controlled Vaporized Cannabis, with and without Alcohol: Subjective Effects and Oral Fluid‐Blood Cannabinoid Relationships. Drug Testing and Analysis. 2015.
  14. Hartman RL, Brown TL, Milavetz G, et al. Controlled Cannabis Vaporizer Administration: Blood and Plasma Cannabinoids with and without Alcohol. Clinical Chemistry. 2015;61(6):850-869.
  15. Gaffney G, Milavetz G, Brown T, Spurgin A, Johnson R. Peak versus Off-Peak Effects of Cannabis: Impacts on Driving Performance. NIDA International Forum; June 12-15, 2015, 2015; Phoenix AZ.
  16. Lee JD, Fiorentino D, Reyes ML, et al. Assessing the Feasibility of Vehicle-Based Sensors to Detect Alcohol Impairment. In. Washington, DC: National Highway Traffic Safety Administration; 2010.
  17. Brown T, Schwarz C, Lee JD, Gaspar J, Marshall D, Ahmad O. DrIIVE Track A: Develop and Evaluate a System of Algorithms to Identify Signatures of Alcohol-Impared Drowsy, and Distracted Driving. 2015. NADS Report N2015-009.
  18. Brown T, Lee J, Schwarz C, Fiorentino D, McDonald A. Assessing the Feasibility of Vehicle-Based Sensors to Detect Drowsy Driving. In. Washington, DC: National Highway Traffic Safety Administration; 2014.
  19. Brown T, Johnson R, Milavetz G. Identifying Periods of Drowsy Driving Using EEG. Annals of Advances in Automotive Medicine. 2013;57:99.
  20. Brown T, McConnell M, Rupp G, et al. Correlation of EEG Biomarkers of Cannabis with Measured Driving Impairment. Traffic Injury Prevention. 2019.
  21. Berka C, Johnson R, Raphael G, Brown T. Phase II Final Report: Quantification of Behavioral and Physiological Effects of Drugs Using a Mobile Scalable Device. Carlsbad, CA: Advanced Brain Monitoring;2015.

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News: Drugged Driving

Dawn Marshall and Tim Brown demonstrate the simulator setup for the alcohol detection study.

Driver monitoring systems (DMS) for cannabis and alcohol detection

Wednesday, January 31, 2024
2023 was a year of driver monitoring systems (DMS) analyses for both cannabis and alcohol detection. DMS projects were collaborations between the University of Colorado, Swinburn University, the Insurance Institute for Highway Safety (IIHS), and Seeing Machines.
2023 Annual Report cover

2023: A Year in Review

Monday, January 1, 2024
Check out our recent highlights and accomplishments from the Driving Safety Research Institute, home of the National Advanced Driving Simulator.
Drugs and Driving presentation slide

Science Café: Drugs and Driving

Friday, April 21, 2023
Tim Brown, Driving Safety Research Institute, and Gary Milavetz, University of Iowa College of Pharmacy, were recent guests of the Science Café, where they discussed drugs and driving.
Tim Brown on KCRG

Univ. of Iowa researchers study drugged driving outcomes

Friday, December 30, 2022
Death and injury among road-users is up to an alarming rate according to a recent study by NHTSA and local researchers. They found that 55.8% of people seriously injured or killed in road crashes tested positive for one or more drugs.
driver in car

New report finds nearly half of Iowa drivers involved in serious crashes tested positive for drugs

Thursday, December 29, 2022
New data from a NHSTA study, in partnership with the University of Iowa, show 45.3% of seriously injured drivers reporting to the Emergency Department tested positive for at least one drug. The top two were alcohol and cannabinoids.
2022 NADS Annual Report cover

2022 Annual Report now available

Wednesday, December 28, 2022
Our 2022 annual report is here! We have spent the past year researching automated vehicles, traffic safety, drugged driving, and much more. Plus, read about our upcoming name change to "Driving Safety Research Institute" on page 3.
Tim Brown, PhD and Rose Schmitt collaborate on testing a driving scenario for an impairment study.

Detecting impairment from cannabis

Wednesday, December 7, 2022
The theme this past year with much of our drugged-driving research has revolved around various methods of detecting driving impairment from cannabis use.
gray and blue screen with white text "surviving bad"

Cannabis Impaired Driving

Thursday, June 16, 2022
Cannabis Impaired Driving. Timothy Brown, Ph.D. Dr. Tim Brown, the Director of Drugged Driving Research at the University of Iowa's National Advanced Driving Simulator joins us to talk about Cannabis and Drugged Driving, and the results are scary.
Woman stepping out of a grey car

Can CBD Impact Your Driving Ability? What We Know

Thursday, June 2, 2022
Millions of Americans regularly use CBD but little is known about the impacts of CBD on driving ability. This Healthline article, with comments from Tim Brown, director of drugged driving research at the National Advanced Driving Simulator, gives insight into driving ability and CBD use.
cannabis dose

Webinar recording: Cannabis and Driving Safety - What's new and what's next?

Thursday, April 21, 2022
Watch a panel discussion of recent research findings on cannabis and driving, including what research is needed to better understand how cannabis impacts driving performance and safety, as well how improved technology might be able to detect impaired driving.
Vehicle with crash damage

Drug use in crashes higher during COVID-19 pandemic

Tuesday, March 8, 2022
The COVID-19 pandemic has changed a lot of things, including the prevalence of drugged driving. The University of Iowa was selected as one of the collection sites to examine the prevalence of drugged driving among seriously and fatally injured road users
Man driving with marijuana in hand

‘Arbitrary’ cutoffs of THC levels make it difficult to measure impaired driving

Friday, January 14, 2022
Knowing if you’re too impaired to drive due to cannabis use is not nearly as straightforward as it is from alcohol use. Finding a way to measure this is a topic of some of our ongoing research.
2021 NADS Annual Report

A year in review: Rural roads, drowsy driving, cannabis, and more

Tuesday, January 4, 2022
See what we’ve been up to in the past year in our NADS Annual Report, with stories about ADS for Rural America, driving drowsy, regenerative braking safety benefits, cannabis and driving, and more. 
Study subject wearing a mobile, wireless X24 EEG headset and completing the Cannabis Impairment Detection Application (CIDA) on a tablet

Researchers identify brain markers that signify cannabis impairment, win ‘top paper’ award

Friday, October 22, 2021
In an important step toward identifying who is too impaired to drive due to cannabis use, a team of researchers from the University of Iowa and Advanced Brain Monitoring found there are specific markers in brain activity linked to cannabis intoxication that consistently and negatively impact driving performance.
Global Road Safety Podcast logo

Podcast: The Latest Research on Drugged Driving with Timothy Brown, PhD

Thursday, October 7, 2021
Research Scientist Timothy Brown, PhD, at the National Advanced Driving Simulator discusses his extensive experience in drugged driving research studies: specifically, his work on the dangers of prescription drug and marijuana use while driving.
a smoker exhaling

Study: Marijuana’s impact on driving is strain-specific

Wednesday, July 7, 2021
In a study published in Traffic Injury Prevention, our researchers found that effects on driving performance after cannabis use can depend on the type of high that the user experiences. Cannabis use that produces more stimulation results in less impact on driving, while use that produces a more stoned or high feeling results in worse driving performance.
A research assistant demonstrates how vaporized cannabis is inhaled using heated air in place of cannabis.

Drugged driving research: Major findings 2010–2020

Monday, December 14, 2020
A quick summary of our major drugged driving research findings from the past 10 years.
Cannabis and driving study example

University of Iowa researchers study effects of cannabis on driving

Wednesday, September 2, 2020
The National Advanced Driving Simulator at the University of Iowa is conducting a paid study to test cannabis users to determine levels of impairment of those who use cannabis.

Advanced Brain Monitoring Hits the Road with Cannabis Impairment Detection

Wednesday, October 2, 2019
Advanced Brain Monitoring is set to develop a Cannabis Impairment Detection Application. Building on successful achievements of a multi-year collaboration with the University of Iowa’s National Advanced Driving Simulator (NADS) involving drug effects on driving and brain activity, the team will conduct controlled cannabis dose-response studies with an alcohol comparison to assess the sensitivity and specificity of the CIDA.

Past findings in NADS cannabis research from 2015

Tuesday, December 1, 2015
Read archived news articles of some of our past research findings in cannabis-impaired driving.