(Click here for a … According to BTS research1, over the past three decades the freight TSI led slowdowns in the economy by an average of 4-5 months. In a new technical report, Transportation Services Index and the Economy—Revisited, BTS reported that the two components of the TSI – the freight index and the passenger index – both lead the economy, although in different ways. Transportation is a reflection of economic activity, inasmuch as products must be moved to markets. Figure 4 shows the relationship between the freight TSI and monthly average retail gasoline prices.