ANN ARBOR—States with high homicide rates also tend to have higher rates of traffic deaths than other states, says a University of Michigan researcher.

In a new study in the current issue of the journal Traffic Injury Prevention, Michael Sivak of the U-M Transportation Research Institute (UMTRI) found that the homicide rate per 100,000 was 5.7 for the 25 states with the highest traffic fatality rates, but only 4.8 for the 25 states with the lowest traffic fatality rates and the District of Columbia. Excluding Washington, D.C., the homicide rate for the 25 states with the lowest traffic fatality rates was 3.8.

“While it is important to note that this result should not be interpreted as implying that a significant fraction of traffic fatalities are homicides, it does suggest that the same aggressive tendencies that contribute to homicides also demonstrate themselves, to a certain degree, in interpersonal behaviors on the road,” said Sivak, a research professor at UMTRI.

Sivak analyzed the disparity in traffic fatality rates per distance driven throughout the United States. He used 2006 data from the Federal Highway Administration, U.S. Bureau of the Census, National Highway Traffic Safety Administration and Centers for Disease Control and Prevention.

He examined 10 factors and found that seven of them accounted for 71 percent of the variance in traffic fatality rates: homicide rates, proportion of male drivers, proportion of older drivers, number of alcohol-related liver failures (as a proxy for intoxicated driving), density of physicians, seat-belt use rate and income.

The strongest predictor of the traffic fatality rates was the homicide rate, which is used in the study as a proxy for aggression.

“This is consistent with the notion that social aspects of human interactions play an important role in traffic safety,” Sivak said. “The overall findings are also consistent with the view that many factors influence the states’ traffic fatality rates. Given that most of these factors are driver-related and a significant proportion of driving is performed across state lines, the variance in road fatality rates is probably as large as could be expected from this type of analysis.”

Sivak found that the average traffic fatality rate was 1.5 deaths per 100 million miles driven in the 50 states and the District of Columbia. Rates ranged from 0.8 fatalities per 100 million miles in Massachusetts to 2.3 fatalities per 100 million miles in Montana.