The Dow Jones Transportation Average is lagging the broader market and the Dow Jones Industrial Average. Add to that, the transportation index is officially in correction territory. Subscribers to the Dow Theory will likely view those points as bad news for broader equity benchmarks.

“Under the so-called Dow Theory, divergence between the Dow Transports—20 companies in the rail, airline and shipping industries—and the Dow Jones Industrials Average has long been followed as an early indicator of trends in the overall stock market. Weakness in companies at the heart of the economy’s supply chain would—so the logic goes—portend looming troubles for the economy and earnings,” according to a recent BlackRock note.

Year-to-date, the iShares Transportation Average ETF (NYSEArca: IYT), the ETF proxy for the Dow Jones Transportation Average Index, is off 11.3% and the largest transportation ETF is getting no help from the industry groups represented in the fund. Stymied by tumbling shares of railroad operators and airlines that have surprisingly fallen in unison with oil prices, transportation exchange traded funds have recently been disappointments. [Transportation ETFs Need Help]

IYT allocates over 45% of its weight to railroad operators, but the major names from that group have posted severe year-to-date losses. For example, shares of Union Pacific are off 21.5%. CSX (NYSE: CSX) has tumbled 14.1% while Norfolk Southern (NYSE: NSC) has plunged 23%. Valuation is playing a role in the transports’ correction, notes BlackRock.

“The recent correction in transports has to be viewed in the context of the index’s 120 percent advance from its 2012 lows. According to Bloomberg data, the two years heading into the end of 2014, the Transport Index posted returns double that of the broader Industrials index. Keep in mind as well that according to Bloomberg data, Transports outperformed by a wide margin during 2014 thanks to several factors: continued growth in e-commerce, lower oil prices benefiting airline earnings and expected crude-by-rail volume growth,” according to BlackRock.