Evaluating the crash and citation rates of Utah drivers licensed with medical conditions, 1992–1996

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Abstract

Background: Medical problems may affect the ability to drive motor vehicles, and programs that control the issuing of driver licenses to individuals with medical conditions exist in most states. The main activity of these programs is the imposition of restrictions upon the driving privileges of individuals with medical conditions that are deemed to pose some risk to public safety. However, little is known about the effectiveness of these licensing programs. Objective: The objective of this study was to compare the rates of adverse driving events (crash, at-fault crash and citations) experienced by drivers licensed with medical conditions to those of age-, sex- and location-matched controls. Separate comparisons were made for drivers reporting medical conditions licensed with full driving privileges, and those with restricted driving privileges (e.g. speed, area and time of day). Design: Retrospective case-control. Methods: The study population was all drivers licensed in the state of Utah who reported a medical condition on their driver license application, over the 5-year period 1992–1996. Drivers enter the program by self-reporting their medical problems. Control drivers were chosen from the entire population of drivers licensed in Utah for the same period. Information on driver license status, participation in the medical conditions program, citations, involvement in crashes, and death certificate data was obtained from the relevant state agencies. Probabilistic linkage methodology was used to link the records in these disparate databases for eventual analysis. Rates of citation, crashes and at-fault crashes, expressed as events per 10 000 license days, were calculated separately for program drivers and their corresponding control groups for each medical condition category and restriction status. These data were used to determine an estimate of relative risk (RR) and 95% confidence intervals. Results: As a group, medical conditions drivers had modestly elevated rates of adverse driving events compared with control drivers (RR 1.09–1.74). Rates in the largest medical category, ‘cardiovascular conditions’, were not higher than controls. Rates were higher than control for some conditions, such as ‘alcohol’ and ‘learning and memory’, for some adverse events (RR 2.2–5.75). Drivers with more than one medical condition appeared comparable to the general group of medical conditions program drivers. Conclusions: Drivers in Utah medical conditions program had modestly elevated rates of adverse driving events compared to matched controls. Possible underreporting of medical conditions and accurate assessment of exposure rates are potential weaknesses in the program.

Introduction

It is intuitive that medical problems may impair one's ability to safely drive a motor vehicle. Thus, nearly all states have specialized licensing programs for drivers with medical conditions, and most states have specific policies related to physical and mental function and driving (Retchin and Anapolle, 1993). Such programs are intended to improve public safety by controlling the driving privileges of individuals whose driving skills are potentially impaired due to medical conditions. However, there are limited data on driving performance for drivers in such programs (Waller, 1965, Davis et al., 1973, Janke, 1993, Medgyesi and Koch, 1995).

Since 1979, the state of Utah has had a licensing program for drivers who have medical conditions. The program was based upon guidelines written by the Utah Driver License Division Medical Advisory Board, a group of volunteer specialty physicians. Their stated goal was to create a program that improved public safety while imposing the fewest possible restrictions on driving privileges for this group of drivers (Beach, 1992). Since its inception over 20 years ago, the program has had little formal review. We therefore, sought to evaluate Utah's driver licensing program by comparing the rates of adverse driving events (citations, crashes and at-fault crashes) of drivers licensed with medical conditions to those of similar drivers without medical conditions over a 5-year period.

Drivers enter into the program by self-report. Utah's licensing program screens all applicants and renewing drivers with a questionnaire on which they are required to identify any medical problems. (The proportion of drivers with medical conditions who fail to report them is unknown.) Medical condition drivers are then placed into one or more of 12 broad medical diagnosis categories as shown in Table 1 (one of the categories, hearing, is assessed only for commercial drivers and is irrelevant for private drivers and was not included in the study). In each category, drivers are assessed to determine the severity of disease process and impairment; this may require an evaluation by a physician. This assessment of driving ability is used to assign drivers to one of 12 functional ability levels, each signifying various restrictions on driving privileges. Functional ability levels may be broadly categorized as permitting one of three actions: applicants may receive an unrestricted driver's license, a driver's license with restrictions (i.e. driving restricted as to speed, area, and/or time of day) or, finally, be entirely denied driving privileges (level 12). (Levels 1 and 2 are used for commercial drivers only.) Specifics of restrictions for a given functional ability level are not totally consistent between medical conditions, but can roughly be summarized as described in Table 2. The functional ability level and the imposition of restrictions are reconsidered each time the license is renewed. License renewal periods are shortened for all program drivers, at both unrestricted and restricted levels, with renewal periods as short as 3 months. The product of the medical conditions program, then, is the imposition of driving restrictions on drivers who, according to the guidelines, have medical conditions that may impair their ability to drive a motor vehicle.

Section snippets

Methods

This study was approved by the Institutional Review Board of the University of Utah Health Sciences Center and by the Utah Resource for Genetic and Epidemiological Research (for the use of death certificate data).

Information used to perform this study was contained in several statewide databases. Driver license data, specifying dates and types of licensure, renewal dates, and citation data were obtained from the Utah Driver License Division (part of the Utah Department of Public Safety). This

Results

During the study period, there were 1 750 918 Utah licensed drivers; 68 770 (4%) of these drivers were licensed in the medical conditions licensing program. The majority of drivers licensed with medical conditions (54 938, 80%) reported one medical condition, while the remainder (13 832, 20%) reported two or more (Table 3). Of this latter group, the majority (77%, 10 595) was licensed in two categories (Table 3). Drivers in the medical conditions program were older than the general population

Discussion

In this study, we have described the rates of adverse driving events over a 5-year period for participants in a statewide, regulatory licensing program for drivers with medical conditions. We found that: (1) overall, drivers licensed with either single or multiple medical conditions had similar rates of citation but higher rates of crash and at-fault crash than their peers; (2) drivers in the largest medical condition category, ‘cardiovascular’, had rates of adverse events no higher than

Acknowledgements

This study was supported by the National Highway Traffic Safety Administration, Grant number DTNH22-96-H-59017.

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