Number 319 November 2006

Traffic Safety Facts

Traffic Tech – Technology Transfer Series

Final Report of Polypharmacy and Older Drivers: 

Identifying Strategies to Study Drug Usage and 

Driver Functioning Among Older Drivers

U.S. Department of Transportation 400 Seventh Street SW., Washington, DC 20590

National Highway Traffic Safety Administration

With the aging population and the number of older drivers increasing,there is concernthatpolypharmacy,taking

multiple medications, might inhibit older people’s ability

to drive safely. To understand the best methodologies

to research the effects of multiple medications on older

driver functioning, the National Highway Traffic Safety 

Administration (NHTSA) contracted with TransAnalytics, LLC to conduct a literature review, a brainstorming

session with subject matter experts, and focus groups

with older drivers. Separate chapters describe the results 

of each project activity and provide guidelines for continuing researchdevelopedfromthese efforts.This report

examines four questions on research methodology.

QUESTION #1

“What is our current understanding of the effects of 

drugs and combinations of medications on crash 

risk or involvement, and which should be the focus 

of continuing research on polypharmacy and driving 

functioning?”

Building on earlier work that identified the most potentially driver impairing (PDI) drugs prescribed to older 

persons (see Traffic Tech, Number 301, 2006), this project narrowed the priorities for further study according

to classes of drugs, not individual medications. With

an emphasis on their exposure in the older population,

as well as their pharmacological actions, the emerging

recommendations for continuing study focus on alpha blockers and other medications used to treat high

blood pressure (anti-hypertensives); sedating drugs 

such as the benzodiazepines, tricyclic antidepressants,

and opioids; and drugs that affect blood sugar levels 

(anti-diabetic agents and drugs that could potentiate

hypoglycemic effects).

QUESTION #2

“What are the most feasible and reliable means of 

measuring and monitoring drug usage—including 

over-the-counter drugs—by older drivers?”

To obtain complete and reliable information from

older persons about their medication regimes, several

factors must simultaneously be addressed: concerns

about the privacy and confidentiality of the information revealed; the personal security of older study 

participants; the credibility of the research team; and 

the overall goals of the study. The recommended approach is a form of the “brown bag” method, where

an older research participant is asked to bring all

of his/her medications (including over-the-counter

drugs) to an office or other neutral location to be inventoried by an appropriate professional. Pharmacists (active or retired) are the best choice, although 

nurses also may have sufficient perceived authority 

and offer a strong “comfort level.” A member of the

research team who can provide assurances of privacy

and confidentiality also should be present during the 

brown-bag interview.

Most desirable is to employ multiple approaches for

measuring/monitoring drug usage among older research participants. A recommended strategy is to

complement the brown-bag review by accessing an

administrative claims (pharmacy) database in which 

the research participant is enrolled. This will provide

a historical record of the individual’s (prescription) 

drug regime that can serve as a screen in participant

recruitment, and provide a valuable point for confirming a participant’s expected drugs and dosages 

during a specific study period.
TRAFFIC TECH is a publication to disseminate information about traffic safety programs, including evaluations,

innovative programs, and new publications. Feel free to

copy it as you wish. If you would like to receive a copy, contact Melissa Cheung, MPH, Editor, fax 202-366-7096, e-mail:

melissa.cheung@dot.gov.

400 Seventh Street SW., NTI-130

Washington, DC 20590

QUESTION #3

“What are the most practical and valid ways of 

assessing the impact of drug use on actual driving 

performance?”

Information about driving functioning can be obtained

through direct measurements of performance behindthe-wheel, in either the participant’s own vehicle or

an evaluator’s (dual control) vehicle, on either a closed 

course or in actual traffic. Simulated driving performance can be measured using a wide range of devices,

from desktop units to fully interactive systems with

motion platforms, high resolution, and a 360-degree

field of view. Indirect measures of the effects of medications on driving performance can be made using clinical assessments of functional abilities most important

for safe vehicle control. Each alternative approach has

strengths and limitations.

A measurement methodology utilizing a combination of approaches is recommended to obtain the most

complete understanding of the (potentially) impairing 

effects of multiple medications, at the highest comfort

levels and the lowest perceived risk by study participants. These include clinical assessments of functional

abilities, using computer-based methods, if feasible,

to promote standardization in test administration and

scoring, and to permit the use of specialized cognitive

tests (e.g., processing speed) that require precise timing. In-vehicle assessment on a closed course with a

properly qualified driving evaluation specialist is recommended, using a dual control vehicle, as a safety

precaution, and a standardized protocol for observation of critical driving skills. To gain an understanding

of how an older person performs in actual traffic conditions while using medications that he or she normally

takes, instrumenting the individual’s own vehicle with

a data collection package that can unobtrusively record

key measures of performance without an experimenter

present is also recommended.

QUESTION #4

“What are the potential barriers to the participation 

of older persons in studies of drug use and driving 

functioning, and how might they be overcome?”

This projectrevealeda number of concerns among older

prospective research subjects. The participation of community-dwelling older persons in studies of the effects

of drugs on driving functioning will be encouraged by

a strong assurance of confidentiality; individuals must 

remain anonymous in reports of the study’s findings, 

and every protection possible under applicable State 

law to shield an individual’s driving performance measures from being made available to a licensing authority must be provided. Informed consent procedures

should specify to study participants all of the parties to

whom the results of their driving evaluations may be

made available.

In addition, the benefits of research participation, for individuals and for society, should be clearly explained.

There appears to be a general willingness on the part

of older persons queried in this project to become involved in research that can improve safety, even if it

requires them to divulge information about the drugs

they are taking and/or to have their driving performance evaluated. Fair compensation for the amount of

time a participant must commit to the study—preferably in cash—also is important.

Conclusions

These guidelines provide a framework within which to

developresearchdesigns for continuing empiricalinvestigations into the effects of drugs on driving performance.

How to Order

For a copy of Final Report of Polypharmacy and Older 

Drivers: Identifying Strategies to Study Drug Usage and 

Driver Functioning Among Older Drivers write to the

Office of Behavioral Safety Research, NHTSA, NTI-130, 

400 Seventh Street SW., Washington, DC 20590 or send 

a fax to 202-366-7096 or download www.nhtsa.dot.gov.

John Siegler, Ph.D. was the task order manager.