CA Department of Motor Vehicles- Licensing Operations Division, Research and Development

One of DMV's core responsibilities is to regulate the driving privilege of drivers who have lost the ability to drive competently and safely. Performing this function effectively and fairly depends upon the ability to validly assess driver competency and identify drivers whose driving privilege should be taken away or restricted. The licensing action that is ultimately taken should secure the safety of the motoring public without unduly restricting the mobility of the driver. Recognizing the importance of mobility in today's society, the department may elect to restrict rather than revoke the driving privilege of a marginally-competent driver. For example, the driver may not be permitted to drive at night, on the freeway, or on any roadway other than a limited number of designated streets in the area of their residence.

R&D recently completed two studies addressing departmental policy related to licensing drivers who cannot pass the standard drive test or have a medical condition that may impair their driving. One evaluated the special drive test (SDT) program, and the other one evaluated the safety impact of licensing visually-impaired drivers who use a bioptic telescopic lens (BTL) device while driving. The findings in these studies have resulted in major changes being made in the SDT and BTL programs.

The study analyzed data collected for 407 drivers referred for an SDT statewide over a 2-week period. The vast majority of these drivers came to the attention of DMV via notification by law enforcement or medical doctors, or contact with a DMV field office in the process of renewing their driver license. Over 90% of the referred drivers had a physical or mental condition reported, most prevalently a vision deficit (22%) or stroke (15%). The average age of referred drivers was 70 years, with 1/5 of the sample being over 85 and 1/5 being under 55. Women represented 42% of the sample.

Other key findings of the study include the following:

test fail rate was 32%;

only 1/4 of all referrals, and 1/4 of all SDT fails, were recommended for a license restriction or other licensing action;

only 14% of drivers who passed the SDT had a license restriction other than corrective lenses on their driving record before, or within 1 year after, the date of the referral;

those who passed the test had subsequent citation and crash rates that were, respectively, 2 times and 3 times higher than the rates for drivers of the same age and sex in the general driving population;

SDT performance was not significantly related to crash risk.

It was concluded that (1) licensing restrictions were being underutilized for incompetent drivers, (2) the SDT lacked validity because it did not discriminate between crash-free and crash-involved drivers, and (3) SDT referrals, even those who pass the test, pose a much higher safety risk than do drivers of similar age and sex in the general driving population. The study recommended that all SDT referrals who are unable to pass the standard drive test (required for novice drivers) should, at a minimum, be restricted from driving at night. It also recommended that SDT referral and testing policies and procedures be reviewed and changed if necessary, and that if the SDT is replaced, the new test should be modelled after California's highly reliable and valid Driving Performance Evaluation (DPE) road test.

Following the SDT study, a multi-divisional task force met to revamp the entire SDT system, including revising the referral criteria, using the DPE as the core road test, and increasing the use of license restrictions. After the new system is implemented, R&D will conduct follow-up evaluations to determine whether the program is operating as intended and producing the desired results.

The second study by Nancy Clarke compared the driving records for all 609 BTL-restricted drivers identified in the driver license masterfile with those for 28,109 non-BTL drivers randomly selected from the same database. The 2-year fatal/injury and total crash rates for the BTL group were found to be 1.7 and 2.0 times higher, respectively, than those for the comparison group after statistically adjusting the measures to account for the influence of age and sex differences between the groups. The BTL group's citation rate, however, was only 0.7 of the comparison group's rate after making the statistical adjustments. All of the rate differences were statistically significant, and even larger differences were found when subjects with expired, suspended, or revoked licenses were excluded in the comparisons. The review of BTL subjects' driving records also revealed that only 35% of these drivers had a sunrise-to-sunset license restriction recorded.

Based on the elevated crash risk of BTL drivers relative to drivers with "normal" vision, the report recommended that the department develop and implement procedures and policies for more effectively assessing and reducing the safety risk presented by BTL drivers. Among the approaches recommended was restricting all BTL drivers to day-time-only driving. The department is also developing improved procedures for assessing the competency of BTL drivers through an improved special drive test.

Copies of the SDT study, "Evaluation of California's Special Drive Test Program" (Report #160) and the BTL study, "An Evaluation of the Traffic Safety Risk of Bioptic Telescopic Lens Drivers" (Report # 163) can be obtained by contacting the California Department of Motor Vehicles' Research and Development Branch, 2415 1st Ave., MS F-126, Sacramento, California, 95818.

Reasearch Notes-Summer 1997