For men and women who have fought in the country's wars in Iraq and Afghanistan, death behind the wheel is becoming another lethal aftereffect of combat.
After they leave military service, veterans of the two wars have a 75 percent higher rate of fatal motor vehicle accidents than do civilians. Troops still in uniform have a higher risk of crashing their cars in the months immediately after returning from deployment than in the months immediately before. People who have had multiple tours to combat zones are at highest risk for traffic accidents.
The phenomenon has been revealed by multiple pieces of evidence - research as well as observations of soldiers, veterans and counselors.
The most common explanation is that soldiers bring back driving habits that were lifesaving in war zones but are dangerous on America's roads. They include racing through intersections, straddling lanes, swerving on bridges and, for some, not wearing seat belts because they hinder a rapid escape.
That's probably not the whole story, however. Post-traumatic stress disorder (PTSD), suffered by thousands of veterans, increases aggressive driving. Drunken driving and thrill-seeking are also more common after combat, according to a few studies and the testimony of many veterans.
If further research supports the observations, motor vehicle crashes will join suicide and interpersonal violence as a fatal, if indirect, consequence of the war on terrorism.
Motor vehicle crashes have long been a serious problem in the military armed services. From 1999 through 2012, a period spanning peacetime and the two wars, as many active-duty military personnel died in noncombat motor vehicle crashes both on and off duty (4,423) as were killed in the Iraq war (4,409).
"Before suicides became the leading cause of non-battle injuries, motor vehicle injuries were," said Bruce Jones, a physician and epidemiologist who heads the Army's injury prevention program at Aberdeen Proving Ground, in Maryland.
War, however, worsens the problem.
Men who served in the wars in Iraq or Afghanistan have a 76 percent higher rate of dying in vehicle crashes, and women a 43 percent higher rate, than similar people in the general population, according to an unpublished study by Han Kang, an epidemiologist with the Department of Veterans Affairs. The same phenomenon was seen in Gulf War veterans and took five years to dissipate.
Fatal motorcycle crashes in particular spiked during the wars. They accounted for 14 percent of military traffic deaths in 2001, but 38 percent in 2008. The absolute rate of motorcycle deaths also tripled over that period.
"A lot of people come home and buy a motorcycle to have that adrenaline rush again," said Steven Acheson, 27, a former forward observer in the Army and an engineering student in Wisconsin.