The workforce in the US has continued its drop as technology-enabled productivity reduces the economic value of older and unskilled workers. While the total size of the workforce is at this writing higher than it was at the depth of the Great Recession, a smaller share of the working age population works today. Fewer people are traveling for work, and fewer discretionary trips are made by both workers nervous about spending money and the unemployed who have little or no money to spend. Starting in 2008 in the US, unemployment increased sharply, and though it has since declined, employment participation rates remain much lower as shown   From Levinson and Krizek (2015) The End of Traffic and the Future of Transport. http://davidlevinson.org/the-end-of-traffic-and-the-future-of-transport/  Figure 3.2 Source; US Department of Labor - Bureau of Labor Statistics (2015) Labor Force Statistics from the Current Population Survey http://data.bls.gov/timeseries/LNS11300000.
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