The median age of automobiles has steadily increased since
1969. In 2005 the overall median age for automobiles was 8.9 years, a
significant increase over 1990 when the median age of vehicles in
operation in the US was 6.5 years and 1969 when the mean age for
automobiles was 5.1 years.

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The United States is home to the largest passenger vehicle market of any country, which is a consequence of the fact that it has the largest Gross Domestic Product of any country in the world. Overall, there were an estimated 243,023,485 registered passenger vehicles in the United States according to a 2004 DOT study.
This number, along with the average age of vehicles, has increased
steadily since 1960, indicating a growing number of vehicles per
capita. The United States is also home to three of the world’s largest
vehicle manufacturers, which are commonly referred to as the "Big
Three." The motor car has become an integral part of American life,
with vehicles outnumbering licensed drivers.

According to the US Bureau of Transit Statistics
there are 243,023,485 registered passenger vehicles in the US. Out of
these roughly 243 million vehicles, 136,430,651 (56.13%) were
classified as cars, while 91,845,327 (37.79%) were classified as "Other 2 axle, 4 tire vehicles," presumably SUVs and pick-up trucks.
Yet another 6,161,028 (2.53%) were classified as vehicles with 2 axles
and 6 tires and 2,010,335 (0.82%) were classified as "Truck,
combination." There were approximately 5,780,870 motorcycles in the US
in 2004, which accounts for 2.37% of all registered passenger vehicles.

According to cumulative data by the Federal Highway Administration (FHA)
the number of motor vehicles has also increased steadily since 1960,
only stagnating once in 1997 and declining from 1990 to 1991. Otherwise
the number of motor vehicles has been rising by an estimated 3.69
million each year since 1960 with the largest annual growth between
1998 and 1999 as well as between 2000 and 2001 when the number of motor
vehicles in the United States increased by eight million.
Since the study by the FHA the number of vehicles has increased by
approximately eleven million, one of the largest recorded increases.
The largest percentage increase was between the years of 1972 and 1973
when the number of cars increased by 5.88%.

According to the US Bureau of Transit Statistics
there are 243,023,485 registered passenger vehicles in the US. Out of
these roughly 243 million vehicles, 136,430,651 (56.13%) were
classified as cars, while 91,845,327 (37.79%) were classified as "Other 2 axle, 4 tire vehicles," presumably SUVs and pick-up trucks.
Yet another 6,161,028 (2.53%) were classified as vehicles with 2 axles
and 6 tires and 2,010,335 (0.82%) were classified as "Truck,
combination." There were approximately 5,780,870 motorcycles in the US
in 2004, which accounts for 2.37% of all registered passenger vehicles.

According to cumulative data by the Federal Highway Administration (FHA)
the number of motor vehicles has also increased steadily since 1960,
only stagnating once in 1997 and declining from 1990 to 1991. Otherwise
the number of motor vehicles has been rising by an estimated 3.69
million each year since 1960 with the largest annual growth between
1998 and 1999 as well as between 2000 and 2001 when the number of motor
vehicles in the United States increased by eight million.
Since the study by the FHA the number of vehicles has increased by
approximately eleven million, one of the largest recorded increases.
The largest percentage increase was between the years of 1972 and 1973
when the number of cars increased by 5.88%.

Via Wikipedia