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Appendix C.
Executive Summary From the First Report, “Evaluating Drivers Licensed with Medical Conditions in Utah, 1992–1996”


Executive Summary

The Utah Driver License Division operates a specialized licensing program for drivers who have medical conditions. The program was developed by the division under the guidance of the Utah Medical Advisory Board. 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, and functional ability level (1-12). The intent of the board 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. Restricted licenses may include speed, area and/or time of day limitations. The functional ability or medical condition categories include:

  1. diabetes mellitus and other metabolic conditions,
  2. cardiovascular,
  3. pulmonary,
  4. neurologic,
  5. epilepsy and other episodic conditions,
  6. learning/memory/communications,
  7. psychiatric or emotional conditions,
  8. alcohol and other drugs,
  9. visual acuity, musculoskelatal abnormalities/chronic medical debilities,
  10. functional motor ability, and
  11. hearing

Utah CODES was funded to evaluate the effect of the existing medical condition licensing program on public safety. The project was funded in part by NHTSA, with the support of the Utah Driver License Division in the Utah Department of Public Safety, and the Utah Department of Transportation.

In order to determine the effects of this public safety program, we compared the citation, crash and at-fault crash rates of drivers licensed with medical conditions to those of similar drivers matched on age group, gender and county of residence. Comparison drivers were obtained randomly from the general driving population and rates of adverse driving events were examined over a five year period, 1992-1996. A two-to-one matching strategy was used. Sampling was performed with replacement.

Analyses were conducted for each functional ability or medical condition category by restriction status. Analyses for drivers licensed with multiple medical conditions were conducted separately, by restriction status. The previous analyses were also conducted separately for drivers who maintained one restriction status during the study period, and drivers whose restriction status fluctuated during the study period. We used probabilistic linkage to link data elements relating to the same driver from several different databases in order to combine the elements needed for the study (i.e., crash, violation and driver license databases).

The rates of citation, crash and at-fault crash varied between the populations and events of interest. Overall, unrestricted drivers licensed with single medical conditions had higher rates of citation, crash and at-fault crashes than the chosen comparison drivers. The differences were statistically significant, but of small magnitude. Restricted drivers licensed with single medical conditions during the study period had higher rates of crash and at-fault crash than unrestricted program drivers, but similar rates of citation. Analysis by individual functional ability categories (medical conditions), showed great variation. Of interest, the citation risk for unrestricted drivers licensed in the categories "cardiovascular" and "pulmonary" had significantly lower rates of citation than their chosen comparison drivers, but similar rates of crash and at-fault crash. The greatest citation risks were found in the restricted categories "learning, memory and communication disorders" and "alcohol and other drugs" where the rates were 11.63 and 5.83 times higher respectively than of the selected comparison drivers. However, these populations were extremely small (N=6 and N=24 respectively) so their impact on public safety was negligible. Similarly, the greatest risks for all crash and at-fault crash occurred in small, restricted driving populations licensed in the "musculoskelatal abnormalities" and "alcohol and other drugs" categories (N=32 and N=24 respectively).

Drivers who were licensed with more than one medical condition during the study period were analyzed separately. The risks for crash and at-fault crash were higher than those of the chosen comparison drivers for both restricted and unrestricted drivers. The magnitude of risk was highest for at-fault crash for drivers who had restrictions imposed on their driver licenses; the rate was 1.76 times higher than those of the chosen comparison drivers (95% CI 1.40, 2.28). The rates of citation for unrestricted drivers were similar and citation rates for restricted drivers were significantly lower than those of their respective comparison groups.

The results of this study provide contextual information on the effects of the medical conditions licensing program on public safety. Specifically, we found that the overall rates of adverse driving events varied between medical condition or category type, and restriction status. Of interest, in the largest functional ability category, cardiovascular (N=18,990), the rates for all adverse events were similar to those of their comparison groups for both restricted and unrestricted drivers; however, unrestricted drivers in this category had a slight but significantly lower rate of citation. For unrestricted drivers, the highest risk of at-fault crash was found in the learning, memory and communications category where the risk of at-fault crash was 3.63 times higher than their respective comparison group (95% CI 2.00, 6.60). The greatest differences in at-fault crash rates were found in restricted license categories. Restricted drivers in the musculoskelatal abnormality or chronic medical disability group had a rate 11.29 times higher than their comparison drivers (95% CI 2.39, 53.25).

As with any injury control intervention, evaluation is an essential component of the program in order to identify areas of increased risk and to provide feedback to the administering agency. Further research should be performed to evaluate the rates of adverse driving events by individual functional ability levels in order to determine if there are distinct levels for which risk increases or decreases, and to describe the effects of co-existing medical conditions for large categories. This information will help to identify areas where the program could be improved, as well as, help to identify functional ability categories where unnecessary restrictions could be eliminated.

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