The U.S. auto industry's new-vehicle sales in 2014 will hit their highest level since 2006 as consumers continue to replace aging cars and trucks, a research firm said today. 

Edmunds.com forecast that sales next year will hit 16.4 million vehicles. That would be up from an estimated 15.5 million the firm expects in 2013 and the highest total since 16.5 million were sold in 2006.

"The average age of all light vehicles on the road climbed to 11.4 years in 2013, and an aging fleet will continue to force buyers back to the market next year," Edmunds chief economist Lacey Plache said in a statement. "With used car prices still elevated over past norms and used car supply still tight, the new-car market will remain attractive."

However, the projected 6 percent growth rate would be the industry's smallest increase since sales bottomed out at 10.4 million vehicles in 2009.