Wednesday, October 08, 2008

Longest Record of Conservation in U.S. History?

The Federal Highway Administration reported that travel during July 2008 on all roads and streets in the nation fell by -3.6% compared to July last year. June marks the ninth consecutive month of traffic volume decline compared to the same month in the previous year. Travel YTD through July in 2008 fell by -3.0% compared to 2007.

There was never more than a single monthly decline in traffic volume (vs. the same month a year ago) until 2006, a few examples of two consecutive monthly declines 2006 and early 2007, but never in the history of these data was there ever a period of more than a 2-month consecutive decline until recently, and therefore the 9 consecutive monthly decline (November 2007 through July 2008) in miles driven is a record, and represents the most significant adjustment to driving behavior in recent history.

On a moving 12-month total basis, traffic volume in July fell to a four-year low of 2.944 trillion miles, the lowest level since July of 2004 (see chart above), and this measure has fallen in each of the last nine months.


At 10/09/2008 7:34 AM, Blogger John Thacker said...

but never in the history of these data was there ever a period of more than a 2-month consecutive decline until recently,

Well, there was in the historic data going back to 1970. Nov. 1973 until Oct. 1974 showed a 12 month consecutive decline in VMT. April 1979 through May 1980 showed declines, with a one-month exception in Jan. 1980 (though then Feb. 1980 was low enough that the 12 month rolling average was below that of Dec. 1979 and indeed below that of Sep. 1978.) These were, of course, the two earlier "gas crises," demonstrating that higher prices will cause conservation.

The first trough, in Oct. 1974, marked a return to the VMT of Mar. 1973 and a decline of 2.1% from the peak of Nov. 1973.

The second trough, May 1980, returned to the levels of roughly August 1978, and a decline of 3.2% from the peak of April 1979.

The current trough represents, as you note, a decline to the levels of July 2004, certainly by far the largest decline "back in the past" of any, although in percentage terms represents a 2.1% decline from the peak of November 2007.

This is largely, however, because VMT had been growing slowly for several years (with rising gas prices) before even the recent declines, as is obvious from the graph. The decline is still not as sharp as in the 1979 gas crisis (which perhaps makes it more manageable), but in terms of comparison to the normal trendline, it's still more impressive.

At 10/09/2008 9:04 AM, Blogger Mark J. Perry said...

Thanks to John Thacker for the pointer to the historic data going back to 1970, I'll update my chart and analysis.


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