Here's the latest sign Americans are making their old cars and trucks run longer. A new study by the auto research firm Polk finds the average age for vehicles in America has climbed to an all-time high of 11.4 years. That's up from 11.2 years average age for the same Polk study reported last year.
The study cited a combination of factors including Americans driving their cars longer due to the slow recovery of the economy and the fact cars and the fact that trucks are more reliable.
These days it's not uncommon for millions of them to keep running 10, 15, or 20 years after they rolled off the assembly line.
Polk calculated the age of the 247 Million cars, trucks and SUV's in operation in America by reviewing Vehicle registrations earlier this year.
Ageing cars & pent-up demand for sales
Americans holding on to their old cars and trucks is one reason auto executives are confident the current surge in new vehicle sales will continue for at least the next 4 or 5 years. The longer people drive their old cars, the greater the pent-up demand for new vehicles and those coming off-lease going into the used car market.
In fact, dealers across the country are already seeing a steady flow of older models being traded in as people finally decide they want or need a new model.
(Read More: America Sets a New Record for Old Cars)
One factor driving that demand will be the growing gap in the fuel economy of vehicles built between 2002 or earlier and the new models. In 2002, the average fuel economy of new cars in the U.S. was 29 miles-per-gallon, according to the U.S. Department of Transportation. By 2012 it was up to 35.6 MPG.
Old and getting older.
Polk believes the number of vehicles at minimum twelve years old will grow at a healthy clip over the next five years. In fact, by 2018 it's estimated the number of vehicles that are at least 12 years old in America will increase by 11.6 percent.
(Read More: The cheapest—and most expensive—cars to drive)
By comparison, Polk forecasts the percentage of cars and trucks under 5 years of age will increase by 41 percent by 2018. That surge is not surprising given the expected rise in new vehicle sales over the next five years.
One market that's not growing, and in fact shrinking between now and 2018, will be models that are 6-11 years old. The number of vehicles in that age group is forecast to decline 21.9 percent according to Polk. That decline is a reflection of the dramatic drop in new vehicle sales between 2009 and 2011.
Questions? Comments? BehindTheWheel@cnbc.com.