The U.S. vehicle population has reached a record-high age after showing rapid gains in recent years, according to Polk, which said this aging fleet and longer ownership periods present dealership service departments — along with other auto repair and aftermarket businesses — with “significant business growth opportunity.”

More specifically, the average age of vehicles currently in operation as of July 1 of 2011 is 10.8 years, compared to 10.6 years on the same date in 2010.

This continues what Polk called a rapid increase over the last five years, climbing all the way up from an average age of 9.7 back in 2006.

“The increasing age of the vehicle fleet, together with the increasing length of ownership, offers significant business growth opportunity for the automotive aftermarket,” stated Mark Seng, global aftermarket practice leader at Polk. “Dealer service departments and independent repair facilities, as well as aftermarket parts suppliers, will see increased business opportunity with customers in need of vehicle service.”

Breaking the data down further, the age of passenger cars climbed only slightly to 11.1, compared to an age of 11 the prior year. Meanwhile, the increase for trucks (10.1 to 10.4) was more dramatic.

Polk explained that this deceleration for passenger car aging reflects the sluggish sales and the car-versus-truck sales mix during 2008 and 2009. During this period, there were a greater number of truck registrations than car registrations.

Officials pointed out, however, that that even though truck sales were stronger during this period, their aging rate was quicker.

That said, the market is likely to see this trend go in reverse in the near future, given the increases in the CUV and small SUV populations over the last two years. What’s more, with new-vehicle sales climbing last year and expectations for those gains to continue, Polk believes the market’s aging rate will probably soften compared to what’s been seen in the last three years.

Moving along, Polk also delved into U.S. vehicle population data. After two years of decreases in vehicle count, 2011 showed an uptick.

Specifically, there were 240.5 million units in operation as of July 1.

After reaching an all-time high of 242.1 million in 2008, the population dropped to 241.5 million in 2009 and 240.0 million in 2010.