Here is the complete series data from 1976. We've added a linear regression (the red line) to further illustrate the direction of the long-term trend.

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In the chart above, the latest moving average value is 21% below its record high in July 2005.

Here is the same chart with two key modifications:

• We've created a per-capita version using the FRED's CNP16OV series for the adjustment.
• We've indexed the numbers so that the first data point, January 1976, equals 100.

  (Click on image to enlarge)

We've repeated these charts using heavy trucks for comparison:

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