It can also highlight important changes in trends and areas of weakness, or red flags. So let's see what these indicators are telling us midway through 2016.

We start with rail intermodal traffic, which registers the long-haul movement of shipping containers and truck trailers by rail whenever combined with (a much shorter) truck movement at one or both ends. This covers a broad range of goods that Americans consume regularly, from laptops to frozen chickens. Since consumption drives the US economy this should give us some clues on recent performance overall.

As in the remainder of our analysis, the grey cloud in the graph above (in units) shows the maximum and minimum volume range recorded for the same week over the five years prior (2011-2015). The green line shows the readings so far this year. And as we can see, these have been quite lackluster since the start of the second quarter, after a strong start of the year. Is this telling us something?