From WardsAuto.com, U.S. vehicle unit sales (in millions) for years 1963-2011 (49 years)are given as:

Cars:

7.72 8.10 9.33 9.03 8.34 9.66 9.58 8.40 10.24 10.94 11.42 8.85 8.62 10.11 11.18 11.31 10.67 8.95 8.49 7.96 9.15 10.32 10.98 11.40 10.19 10.55 9.78 9.30 8.18 8.21 8.52 8.99 8.62 8.48 8.22 8.08 8.64 8.78 8.35 8.04 7.56 7.48 7.66 7.76 7.56 6.77 5.40 5.64 6.09

Trucks:

1.27 1.39 1.55 1.64 1.55 1.83 1.97 1.81 2.10 2.63 3.15 2.69 2.48 3.18 3.68 4.11 3.48 2.49 2.29 2.58 3.16 4.16 4.75 4.92 5.00 5.24 5.07 4.85 4.36 4.90 5.68 6.42 6.50 6.98 7.28 7.88 8.78 9.03 9.12 9.10 9.41 9.82 9.78 9.29 8.90 6.72 5.20 6.14 6.95
 

Total:

8.99 9.49 10.89 10.66 9.88 11.49 11.55 10.21 12.34 13.57 14.57 11.54 11.10 13.29 14.86 15.42 14.15 11.44 10.78 10.54 12.31 14.48 15.73 16.32 15.19 15.79 14.85 14.15 12.55 13.12 14.20 15.41 15.12 15.46 15.50 15.97 17.41 17.81 17.47 17.14 16.97 17.30 17.44 17.05 16.46 13.49 10.60 11.77 13.04