Weakness in the Dow Jones Transportation Average, which is the oldest stock market index, has “bearish implications,” according to Mark Hulbert of MarketWatch. A recent U.S. Department of Transportation report concluded that, over the past three decades, the index “led slowdowns in the economy by an average of four to five months.” Hulbert also cites “Dow Theory, the oldest stock market timing system in widespread use today,” and its proponent, Jack Schannep, who gave a “sell” signal Friday. Hulbert notes that the Transports Index have been “breaking down in a big way” and that it peaked at an all-time high last month.  Thus, he concludes: “Insofar as the index continues to be a reliable leading indicator . . . the economy and stock market may be living on borrowed time.”