U.S. flag

An official website of the United States government, Department of Justice.

Drug-Impaired Driving: NIJ-Sponsored Panel Points to Priority Needs for Addressing Complex Enforcement Challenges

As more states legalize marijuana, the search for better methods of proving and preventing drug impairment on the road accelerates.
Date Published
April 15, 2021

Drug-impaired driving is risky behavior. The fact that many Americans fail to recognize that risk makes it all the more dangerous — especially when they decide to get behind the wheel while under the influence of drugs.[1]

Making matters worse is the daunting challenge facing those in the criminal justice system tasked with detecting and prosecuting drivers impaired by drugs other than alcohol.

For alcohol impairment, years of robust data have reliably established specific, detectable levels of blood alcohol associated with impairment. In contrast, for other widely available drugs, both legal and illicit, to date the data are insufficient to establish enforceable impairment markers. For instance, as yet there are no reliable markers to definitely establish impairment by THC and other marijuana components.

For the criminal justice system, developing effective policies, practices, and standards to fight drug-impaired driving means first building a firm foundation of priority research needs for law enforcement, forensic toxicology, prosecuting agencies, and practitioners.

Taking a Multi-Disciplinary Approach to Ranking Research Needs

Toward that end, NIJ held a workshop in which expert law enforcement officers, toxicologists, and prosecution officials identified and ranked top needs for relevant research. Researchers from the RAND Corporation (RAND) and RTI International (RTI) facilitated the workshop, part of the NIJ-sponsored Priority Criminal Justice Needs Initiative.

Select examples of high-priority justice system needs identified by the expert panel are:

For law enforcement

  • For each agency, identifying the right number of officers with specialized training in identifying drug impairment.
  • Developing more observational tests for the standard field sobriety battery.
  • Developing training to boost the confidence of law enforcement officers called to testify in drug cases.

For forensic toxicologists

  • Identifying gaps in funding and other resources for forensic toxicology labs to meet capability requirements and demand.
  • Establishing training for toxicologists on interpreting test results in driving under the influence of drugs cases.

For prosecutors

  • Providing more access to training, given that drug-impairment cases are among the most technical and difficult to litigate.
  • Identifying best practices for dealing with drivers’ refusal of impairment tests.

(See complete list of priority needs in “The 13 Top-Tier Needs” below.)

The Challenge of Identifying Drug-Impaired Driving

Existing Tools Have Benefits and Drawbacks

The panel emphasized the primary importance of establishing a suspect’s drug impairment, even absent a means to detect the amount of drug in the suspect’s system, according to the workshop panel’s report. Tools commonly deployed to assess drug impairment, and key benefits and drawbacks of those tools, include the following:

Benefits and Drawbacks
Tool Benefits Drawbacks
Officers specially trained to detect drug impairment, drug recognition experts Can be very effective in characterizing impairment. Many jurisdictions have too few drug recognition experts.
Standardized field sobriety tests Are often effective in detecting impairment. Additional observational tests might be needed.  

Officers must be prepared to present observational evidence in court.  
Roadside chemical tests Can be helpful in informing the decision on impairment. No roadside chemical test will cover all drugs. 

A negative roadside test does not rule out impairment.  
Laboratory-based toxicological screening Can provide powerful evidence of drug detection.   The utility of laboratory screening can be reduced by delays, laboratory backlogs, and insufficient training of toxicologists to interpret data in court testimony.  

Generally, scientific evidence of the amount of a substance in an individual’s system cannot establish impairment, especially in cases of multiple drug use.  

Evidentiary Challenges in Drug-Impaired Driving Cases

The incidence of drug-impaired driving has risen in recent years, even as more states moved to legalize cannabis for recreational and medicinal purposes in several states, according to the research report. In 2017, 12.8 million individuals drove under the influence of drugs alone, up 9% from the previous year, according to the federal Substance Abuse and Mental Health Services Administration. Cannabis-related impairment is second only to alcohol in impaired-driving statistics. Studies have shown that states that have legalized cannabis use have experienced increases in traffic deaths after the opening of cannabis stores.[2]

Given those trends, new urgency has attended enforcement of laws against drug-impaired driving. But solutions need to be able to withstand evidentiary challenges. In contrast to alcohol, which can be detected in the system up to 12 hours after ingestion, THC, the chemical component of cannabis associated with impairment, can quickly dissipate in the system. Some cannabis elements, on the other hand, are detectable long after any impairment has worn off.

Further complicating enforcement is the absence of any fixed threshold of THC concentration in blood signaling user impairment — unlike the 0.08% blood alcohol level widely accepted as evidence of alcohol impairment. Prosecutors are challenged by the fact that many courts tend to view such tests as evidence of drug use only, and not per se proof of impairment, unless concentrations are very high. “Because of these limitations,” the report said, “observational field tests performed by skilled law enforcement officers who make contact with the suspect are a critical piece of evidence, which, along with chemical tests (that provide corroboration), can support a finding of drug-related impairment.”

Another variable is inconsistent evidentiary standards among the states, with some states adopting certain drug concentrations as evidence of potential impairment, and others taking a zero-tolerance approach — that is, one where any detectable amount of a substance is deemed evidence of impairment.

Three types of training are available for officers to perform observational drug tests: drug recognition expert certification, standardized field sobriety test training, and an advanced roadside impairment test training course developed by the National Highway Traffic Safety Administration. In all three areas, however, admission of evidence in court can be problematic if the officer deviates from protocols.

The Expert Panel on Priority Needs: Method and Product

To compose the workshop panel, RTI researchers reviewed relevant literature to identify experts from law enforcement, forensic toxicology, and prosecutor offices. Workshop invitations were based on publication records, leadership roles, or recommendations from other experts. Participants reviewed literature on drug-impaired driving issues to prepare for the workshop, where they discussed protocols, limitations, and challenges they face in collecting and interpreting evidence. The panelists then ranked research needs that emerged from the discussions.

In ranking needs by priority, the workshop team used a blended weighting technique developed by RAND that balanced the perceived importance of each need against the probability of achieving that need, if prioritized. The higher the assigned importance and the higher the perceived probability of success, the higher the priority assigned to that need.

In the end, the experts identified and ranked a total of 29 high-, medium-, and low-priority needs, with 13 identified as top-tier, or highest-priority, needs. The 13 top-tier research needs and associated problems or opportunities are presented below.

The 13 Top-Tier Needs

Law Enforcement Needs
Problem or Opportunity Associated Need
In many jurisdictions, there are not enough officers with access to training through the Advanced Roadside Impaired Driving Enforcement program or the Drug Recognition Enforcement certification program. Identify the likely benefits from having the “right” number of trained officers.
Additional observational tests are needed to enhance DUID detection. Add more observational tests to the standard field sobriety testing battery.
Obtaining warrants often delays timely blood draws. Conduct research to identify the barriers to adoption of e-warrants and the costs, risks, and benefits of implementation.
After obtaining authorization, timely blood draws are sometimes difficult to get. Identify the costs, risks, and benefits of alternative phlebotomy approaches (e.g., officer training, contracts).
Field sobriety tests are effective, as long as standard protocols are followed. Collect detailed data on the effectiveness of field sobriety tests when used for actual DUID cases for use in additional research.
Officers often are not prepared to go to court. Develop and validate training to boost the confidence of officers when testifying (e.g., “cops and court” training).
Forensic Toxicology Needs
Problem or Opportunity Associated Need
Toxicology labs are unable to do an adequate job with respect to the scope and sensitivity of DUID testing. Identify the gaps in resources and potential funding sources that could bring labs up to the required capability.
There are not enough toxicologists to provide DUID consultation and testimony involving interpretation of toxicology test results. Promote and improve access to interpretive DUID training for toxicologists (ideally jointly with prosecutors).
There is a significant number of jurisdictions that are not receiving toxicology results in a sufficiently timely fashion. Identify the impact and risks to justice and due process of not investing sufficient resources into toxicology testing.
Prosecution Needs
Problem or Opportunity Associated Need
Drug impairment cases have become some of the most technical and difficult to litigate for law enforcement officers, forensic toxicologists, and prosecutors. Collect solutions that could increase prosecutors’ access to training for technically complex DUID cases.
There are several technical issues related to the prosecution and evaluation of DUID cases that would benefit from additional research. Collect and identify critical research areas, for example, research establishing the effectiveness of using validated observational field tests and identifying successful means of addressing the technical complexity of DUID cases.
The right to refuse testing can make the evaluation of impairment for DUID cases more difficult (for example, standardized field sobriety tests and chemical testing, such as body fluid and toxicology testing). Identify best practices for dealing with refusals.
Loss of implied consent is likely to lead to additional risk as it becomes harder to enforce existing law. Highlight the risks and benefits of changing implied consent laws and implementing other possible solutions, such as e-warrants.


 Signs and symptoms of drug-impaired individuals vary, and proving impairment can be a complex undertaking. Standardized observational tools and chemical tests, however, can yield legally sufficient proof of drug-impaired driving, the report noted. Collaboration across fields is critical to adequate enforcement, as is the education of judge and jury by prosecutors on how to weigh observational and chemical evidence under a totality-of-the-circumstances standard of proof.

About This Article

The research described in this article was funded by NIJ award 2018-75-CX-K006, awarded to the RAND Corporation (RAND), as part of the Priority Criminal Justice Needs Initiative (PCJNI). PCJNI is a project of RAND, RTI International (RTI), the Police Executive Research Forum, and the University of Denver, under direction of the National Institute of Justice. RAND and RTI managed the activities described in this report. This article is based on the grantee final report, Countering Drug-Impaired Driving: Addressing the Complexities of Gathering and Presenting Evidence in Drug-Impaired Driving Cases, by Camille Gourdet, Michael Vermeer, Michael Planty, Duren Banks, Dulani Woods, and Brian Jackson.

Date Published: April 15, 2021