An improved housing market benefits the auto industry in three ways, Edmunds.com economist Lacey Plache said on the Tuesday conference call. One is that "truck sales and housing starts are closely correlated (because) as construction work increases, workers will replace their aging trucks." The average age of the U.S. truck fleet is 10.4 years, while the useful life of a truck is estimated at 15.5 years, Edmunds said. Additionally, rising housing values create a "wealth factor that is translated into auto sales," and refinancing, driven by lower interest rates, is providing U.S. homeowners with average monthly savings of $210, which can be allocated towards a new car payment. Meanwhile, Nesvold said expectations of a new F-150 rollout helped to fuel the rally in Ford shares at the end of 2012. In December, Ford shares rose 12%, GM rose 10% and the S&P 500 rose marginally. The chief factor in the rise of the two automakers was the government's decision to sell its remaining GM shares," he said. "The GM rally dragged Ford shares higher." In addition, "there's been a bias against Ford in the market by some investors," based on the theory that GM will benefit more from the cyclical housing improvement than Ford will because of its new Silverado, Nesvold said, adding, "To some degree, the F-150 concept might ease this perceived overhang on Ford." Follow @tedreednc-- Written by Ted Reed in Charlotte, N.C.