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Medical Conditions And Crash Risk: Do Restrictions On Licenses Have An Impact On
Public Safety?

falriC Satety Facts

dt ic Tech — Technology Transfer Series

Number 219 April 2000

U.S. Department of Transportation
National Highway Traffic Safety Administration
400 Seventh Street, S.W., Washington, DC 20590

MEDICAL CONDITIONS AND CRASH RISK: DO RESTRICTIONS
ON LICENSES HAVE AN IMPACT ON PUBLIC SAFETY?

In Utah, there is a special licensing program, developed under the guidance of the Utah Medical Advisory
Board, for drivers who have certain medical conditions. The program's guideline describes the physical,
mental, and emotional capabilities appropriate for various types of driving, and determines license eligibility
by medical condition or functional ability category. The intent was to create the least restrictive program
possible that was consistent with public safety. Drivers who are licensed with medical conditions may
receive a full unrestricted or restricted license depending on their functional ability level. Restrictions may
include speed, area, or time of day limitations. Do drivers with certain medical condition restrictions have
more crashes or citations than other drivers?

Utah is one of the seven original states to participate in the Crash Outcome Data Evaluation Systems
(CODES) project. Briefly, CODES links crash data describing the details of each crash in the state
(generated from the police crash report) with other information like medical and financial information
collected at the time of treatment. These data provide information about the nature, cause, and costs of
injury resulting from motor vehicle crashes.

Using probabilistic linkage and several different databases, Utah CODES researchers were able to link
information on drivers with certain license restrictions to their crash and traffic citation history. The National
Highway Traffic Safety Administration (NHTSA) supported the study along with the Utah Driver License
Division and the Utah Department of Transportation.

This study evaluated the crash risks of more than 68,770 drivers in the state of Utah who were licensed
with medical conditions. Drivers who were licensed with medical conditions were matched to comparison
drivers from the general population of drivers, using age, sex, and county of residence as matching factors.
The driving records of all of these drivers were used to find the citation, crash, and at-fault crashes for the
five years between 1992 and 1996.

Increased Crash Risk

When viewed as a whole, drivers who were licensed with medical conditions had higher risks across
crashes, violations, and at-fault crashes than the comparison drivers. Comparisons were not made within
medical condition categories because there were often not enough drivers to make comparisons.

Putting It Into Perspective

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There were categories in which all drivers, both restricted and unrestricted, showed consistently higher
risks for crashes, citations, and at-fault crashes: alcohol and other drugs andvision.

There were also categories where restricted drivers performed better than their unrestricted comparison
groups in both crash rates and at-fault crash rates: diabetes and other metabolic conditions; pulmonary
conditions; neurological conditions; learning, memory and communication disorders. While the restricted
drivers had higher crash rates, they had citation rates similar to their comparison groups. One conclusion is
that it might be logical for licensing agencies to consider raising the bar by imposing restrictions at lower
levels of functional impairment than is currently the case. Based on crash risk factors, priority categories for
evaluating restriction levels include: learning, memory and other communication disorders; psychiatric and
other emotional conditions; alcohol and other drugs; and musculoskeletal abnormalities.

These findings will be useful to state licensing authorities in determining appropriate level of restriction for
various conditions. Any injury control program must have a multi-faceted evaluation program that is fair to
the drivers with medical conditions, and to the interests of safety. In addition, it is unlawful for any State or
local government under the Americans with Disabilities Act to discriminate against a qualified person with
disability on the basis of those disabilities.

HOW TO ORDER

For a copy of Evaluating Drivers Licensed with Medical Conditions in Utah, 1992-1996, (44 pages
plus extensive appendices) write to the Office of Research and Traffic Records, NTS-31, NHTSA, 400
Seventh Street, S.W., Washington, DC. 20590, or fax (202) 366-7096. John Eberhard, Ph.D., and Essie
Wagner were the contract managers.

Single Functional Ability Category and Comparison Groups with a Single Restriction Status

Condition or Disorder License || At-Fault Crash Rate |] Relative At-
Status 5 7 Fault
Medical ‘Comparison 5
Conditions Group Crash Risk
Diabetes Not 1.00 0.69 1.44 *
Restricted
[Restricted || 1.10 ll 0.31 I 3.56 ]
‘Cardiovascular Not 0.55 0.55 1.00
Restricted
[Restricted || 2.04 ll 1.08 l| 1.88 ]
Pulmonary Not 0.85 0.68 1.25 *
Restricted
[Restricted || 0.43 ll 0.61 I 0.71 ]
Neurologic Not 1.26 0.60 2.10 *
Restricted
[Restricted || 0.88 ll 0.91 l| 0.96 ]
Epilepsy Not 1.53 0.82 1.86 *
Restricted
[Restricted || 2.22 ll 0.78 L 286* |
Learning, Memory and Not 2.22 0.82 2.72 *
Communication Restricted
[Restricted || 0.00 ll 0.00 || zero rate |
Psychiatric Not 1.35 0.71 1.80 *
Restricted
[Restricted || 2.70 ll 1.35 I 2.00 ]
Alcohol and Other Drugs Not 1.67 0.72 2.33 *
Restricted
[Restricted || 7.98 ll 1.30 | Cae
Vision Not 1.14 0.75 ] 1.51 *

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Restricted _ || | I |

[Restricted || 1.19 ll 0.75 | 160* |
Musculoskeletal Not 1.03 0.54 1.90 *

Restricted

[Restricted ll 0.00 ll 0.00 l| zero rate ]
Functional Motor Not 1.18 0.66 1.80 *

Restricted

[Restricted l| 0.00 ll 1.27 I zero rate ]

lrate calculated per 10,000 license days.

* statistically significant at the .05 level

U.S. Department

of Transportation

National Highway

Traffic Safety

Administration

400 Seventh Street, S.W. NTS-31
Washington, DC 20590

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:
Linda Cosgrove, Ph.D., Editor, Evaluation Staff

Traffic Safety Programs
(202) 366-2759, fax (202) 366-7096
mailto :lcosgrove@nhtsa.dot.gov

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