IYT tracks an index that invests solely in companies defined by GICS as transportation. The following sub-industries are included: air freight & logistics, airlines, airport services, highways & rail tracks, marine, marine ports & services, railroads, and trucking. Eligible securities must be included in the S&P Total Market Index and must meet certain liquidity and capitalization thresholds. All eligible securities are then selected for inclusion in the index. Securities in the underlying index are also float market cap weighted, subject to certain capping requirements. A maximum weight of 22.5% of the fund can be allocated to one company, and the aggregate weight of all issuers that individually exceed 4.5% of the index weight are capped at a maximum of 45%. Rebalancing is done on a quarterly basis. Prior to July 19, 2021, the fund tracked the Dow Jones Transportation Average Index.