The cost of mayhem on the nation’s most congested roads in and around Washington — those fender benders, the medevacs, the lawsuits and lives lost — now has a price tag: $7.4 billion a year.

That is the cost calculated in the latest crunching of statistics from the region, taking into account 350 traffic deaths and 42,566 injuries recorded in 2009 by the National Highway Traffic Safety Administration.

If any good news can be found in this latest attempt to quantify the damage done to lives and property, it might be that, apportioned per capita, crashes cost less in this area than they do nationwide.

That’s apparently because the slow-speed accidents of cars caught in congestion do less damage and cause fewer deaths and injuries than those that occur at highway speeds.

The report was conducted by Cambridge Systematics for AAA.

Researchers say there is a silver lining to Washington’s gridlock: Slow-speed accidents cost less. (Mark Gail/WASHINGTON POST)

Researchers concluded that the cost per capita of a crash in this region is $1,363, compared with a national figure of $1,522.

“There is a silver lining,” said John B. Townsend II of AAA. “It doesn’t cost as much because we can’t go as fast.”

The overall national cost was pegged at $300 billion.

To draw their local conclusions, the researchers examined federal crash data from the same area that the U.S. Census Bureau uses to define the Washington region.

It includes the District and the cities of Alexandria, Fairfax, Falls Church, Manassas and Manassas Park, plus the counties of Arlington, Charles, Fairfax, Loudoun, Montgomery, Prince George’s and Prince William.

Figuring out the cost of an accident requires more than adding the medical and auto body shop bills.

Researchers used sophisticated federal guidelines that place a value on a lost life, and consider lost wages, time lost on the job, effect on the quality of life and other factors.

But the cost of congestion to Washington drivers was ranked fourth highest in the nation at almost $3.9 billion a year in the Texas Transportation Institute’s annual report for 2011.

That study — which said Washington had the worst congestion in the United States — put the annual additional cost of commuting in rush hour here at $1,495.

The institute, which is based at Texas A&M University, in College Station, found that Washington drivers were spending more than three days a year caught in traffic.

The Census Bureau confirmed the grip of gridlock on the region, determining that Maryland drivers, thousands of whom drive to work in the District or Virginia, have the longest average commute in the nation.