When then Secretary Norman Mineta rang the opening bell at the New York Stock Exchange in 2004 to announce a new monthly transportation index, he kicked off a new era in the use of statistics for measuring transportation. In the decade since, the Bureau of Transportation Statistics, the DOT’s data agency, has been applying its advanced statistical methods to track the level of transportation activity, issuing an index number every month.

During the past 11 years, the BTS Transportation Services Index (TSI) has shown the changes in transportation activity, including both its low in the 2007-2009 recession and its record highs in recent months.

Transportation Services Index (TSI) Freight and Passengers (Year 2000=100)

The Freight Transportation Services Index  measures freight shipments and is an excellent gauge of the economy. In recent months, the seasonally-adjusted index has remained close to the November 2014 all-time high except for a slip during the winter’s severe weather. In fact, earlier this month, BTS announced that freight activity in March had bounced back from the weather-related February decline and was less than one-half of 1 percent below the November record.  It's also up a full 23 percent since hitting a recession low in April 2009.  A separate Passenger Travel TSI his grown 10 percent since the recession.

Our work on the TSI is a major step forward not only because of the index's ability to track whether transportation has grown or declined in past months. The TSI also demonstrates a leading relationship to changes in the business cycle and economic growth. For example, the freight index tends to turn down before economic growth slowdowns, that is, when the economy may be growing but not as fast as in previous months. The passenger index turns down before recessions, which is when the economy contracts. 

At BTS, we are proud that the Conference Board, a respected voice in economic discussions, has recognized the importance of the TSI by including it its database of global business cycle indicators. The Conference Board also recognized the TSI in its March Business Cycle Indicators report.

In addition the Federal Reserve Bank of St Louis included the TSI in its widely-used FRED database of economic indicators.

So, the next time your read of movement in our Transportation Services Index, remember that it's more than just the number of trucks on the road; it's a vital statistic measuring the flow of goods and passengers through America's economy.

Patricia Hu is Director of the Bureau of Transportation Statistics.