Warren Buffett's 'desert island' indicator is sending a not-so-good signal about the economy

Last week, we pointed out that railcar traffic - the one indicator Warren Buffett would want on a desert island to tell how the economy is doing - is the weekly indicator most connected to quarterly GDP.

Well, this week's numbers don't make staying on the island look too bad.

Railcar traffic was down 1.9% during the week ending June 13 from the same week in 2014, according to the report from the Association of American Railroads.

Carloads, which according to the Department of Transportation transport bulk commodities like coal and agricultural products, shrank 8.1% compared to this week last year and is down 3.4% year to date. The biggest dropoffs came from energy products, coal especially, which echoes the current difficulties of that industry.

Intermodals, which the DOT says transport all sorts of finished products from bicycles to greeting cards, went up compared to last year and is up in 2015. But it was not enough to offset the carload losses.

This week's losses were less than last week, where the decrease was 2.1%, and the total numbers have improved over May but still show a slower 2015.