Bus drivers in San Francisco hardly ever drink on the job, but about one quarter reported a drinking problem, according to a study published in the July issue of Alcoholism: Clinical and Experimental Research.

On-the-job stress may be driving them to drink, according to researchers.

Bus drivers contend with a variety of daily stressors, and the more years drivers logged behind the wheel, the more likely they were to report a drinking problem. The connection between years of driving and alcohol problems suggests that drinking might stem from job conditions, according to the study.