Yesterday in options trading we saw an influx of bearish put buyers in iShares Dow Jones Transportation Average (NYSEArca: IYT) as the exchange traded fund itself traded very heavy volume over 1 million shares versus its typical average.

IYT has slightly lagged the broad U.S. equity market year to date, as the ETF is up 6.15% year to date versus the S&P 500 Index up 7.40% so it is possible that holders of the ETF are purchasing downside protection through the puts, or the activity could also be outright bearish speculation.

Current top holdings in IYT are UNP (12.08%), FDX (9.06%), NSC (8.31%), UPS (8.06%), and ALK (8.00%) and the fund remains one of four current alternatives in the ETF space that are in the “Transportation” sector.

SPDR S&P Transportation (NYSEArca: XTN) is newer to the ETF universe, as the fund debuted a little over a year ago, in late January of 2011. Unlike IYT which tracks a Dow Jones Transportation Average index, XTN is based on an S&P index. Since XTN’s inception, IYT has outpaced it handily, up 5.29% versus XTN losing 0.35%.

Two other funds that fall within the “Transportation” category are not broad based plays like IYT and XTN, but instead are focused specifically on the Airlines and Shipping industries.