The Department of Transportation has produced a piece of research that to a limited extent supports its claim that truck driving contributes to a shorter life expectancy than other occupations.

Both Transportation Secretary Ray LaHood and Federal Motor Carrier Safety Administration chief Anne Ferro have said that the life expectancy of a commercial driver is 16 years shorter than the norm.

The issue came up in the context of concern about driver health as a consequence of the demands of the job and behaviors such as cigarette smoking.

DOT answered an inquiry about the source of that 16-year difference with two studies, neither of which supported the statistic.

Now Martin R. Walker, chief of research at FMCSA, has forwarded another study that measured mortality among unionized truck drivers and dock workers.

The study, "Cause-Specific Mortality in the Unionized U.S. Trucking Industry," was published in the August 2007 edition of Environmental Health Perspectives. It was based on an analysis of the records of about 54,300 employees of four unionized trucking companies in 1985.

The key finding was that the workers had higher rates of lung cancer and heart disease than the average population, possibly as a consequence of exposure to diesel and propane exhaust.

One of the demographic measurements in the study was the mean age of death: among the cohort of drivers it was 61.3, plus or minus 8.6 years; and among the non-drivers it was 59.1, plus or minus 10.6 years. The median age of death for both groups combined was 61.9 years. The median age of death for men nationally in 1992 was 73.2 years.